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Guidebook for Conducting Airport User Surveys (2009)

Chapter: Chapter 5 - Air Passenger Surveys

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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 5 - Air Passenger Surveys." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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73 A survey of air passengers involves a number of difficult challenges because of the wide range of information that may be required and the limited opportunity to perform the survey, given that the subjects are anxious to catch their flight. Thus air passenger surveys require careful atten- tion to survey methodology and development of an effective sampling plan and questionnaire. Related aspects that are also addressed in this chapter include gathering information on greeters and well-wishers and on the use of ground vehicles for planning airport groundside facilities. 5.1 Purpose of the Survey Much of the information about air passengers that is needed for planning or operational deci- sions cannot be directly observed or is not readily available from statistics that are collected rou- tinely; it can only be obtained by asking the passengers themselves. Surveys of air passengers are the most common type of airport user survey and are performed for a variety of reasons, includ- ing data collection on the following: • Air party characteristics for airport terminal planning. • Air passenger use of ground transportation for airport groundside15 planning and regional transportation planning. • Air travelers’ choice of airport in a multi-airport region. • Air passenger satisfaction with airport facilities or services. An air passenger survey may be initiated to gather information on a very specific issue, such as the use of different ground transportation modes in order to perform an air quality emissions analysis for environmental impact documentation of an airport project. However, given the cost and effort involved in performing a survey, consideration should be given to whether there are other information needs that can be met at the same time by expanding the scope of the planned survey. Such scope expansion will require a careful tradeoff between the need for the additional information and the potential impact on the cost and complexity of the survey. The information obtained from air passenger surveys is so important to airport planning and management that many airports perform such surveys on a regular basis, such as every year. These surveys often contain the same core set of questions in order to provide a consistent time C H A P T E R 5 Air Passenger Surveys 15 Also often referred to as landside planning. However, the term landside can also refer to airport terminal facilities, as distinct from airside facilities that handle aircraft. The terms landside and airside are also sometimes used to refer to the areas of the passenger terminal before and after security screening. For these reasons, the term groundside is less ambiguous and is used throughout this guidebook to refer to those areas of the airport used by ground access and egress vehicles, including the ter- minal curbfront, airport roadways, and vehicle parking facilities.

74 Guidebook for Conducting Airport User Surveys series of information, but questions may be added to a specific survey to address particular issues of interest at the time. One important role of air passenger surveys is to provide information on air traveler charac- teristics and decisions in order to develop models for air travel demand forecasting, airport ground access mode choice, and airport choice. These models play an important technical role in airport planning, regional transportation planning, and airport system planning studies and generally require very detailed data on a large sample of individual air travel parties. Table 5-1 illustrates the range of information obtained in a representative sample of air pas- senger surveys undertaken prior to the drop in traffic following the events of September 11, 2001. Although the travel environment has changed since 2001, the types of information shown in the table remain valid. The purpose for which the survey is being undertaken influences a wide range of survey plan- ning decisions, including how and where the survey will be performed, the questions that will be asked, the sample size required, and the sample strategy adopted. Therefore, the purpose needs careful thought at the start of the survey planning process. 5.2 Survey Methodology The circumstances under which air passengers spend time at an airport have an important influence on the choice of survey methodology. Passengers are available to be surveyed for only a relatively short time and may have activities they need or wish to undertake during this time. Departing passengers are concerned that they not miss their flight, while arriving passengers may have people waiting to meet them or be anxious to claim checked bags and be on their way. These constraints determine how passenger surveys can be performed. The three principal decisions on survey methodology are as follows: • Whether to interview passengers or use self-completed survey forms. • Where to perform the survey. • When to perform the survey. There are a number of issues specific to air passenger surveys that need to be considered in planning the survey and designing the questionnaire, including how to account for air passen- gers traveling together and the variation in air travel characteristics by time of the day and day of the week. 5.2.1 Issues Specific to Air Passenger Surveys The first issue to consider is that air passengers often travel in groups, referred to as air travel parties, so it is important for surveys to collect information on the composition of the air travel party. Whether it is best to collect data on the basis of the air travel party or from air passengers as individuals is really a function of the survey methodology. Self-completed surveys are typi- cally given to every adult passenger, because it may not be obvious who is in the same party when the questionnaires are distributed. Handing out questionnaires to every passenger is fairly low cost and helps improve the response rate, because some passengers may not complete the sur- vey. If the survey involves survey staff interviewing respondents, typically only one representa- tive from each party is interviewed. It makes no sense to ask the same questions of other members of the same party, although there are a couple of caveats to this. The first caveat is that with large air travel parties, such as tour groups, an interview survey may get multiple responses from the same party, because the members of the party may not be

Air Passenger Surveys 75 standing or sitting together and it may not be obvious who is in the party. Indeed, it may be desir- able to get multiple responses from the same party because their characteristics may be different (e.g., they may have traveled to the airport separately). This situation leads to the second caveat. There may be a difference between the air travel party (often shortened to air party) and the ground access party (e.g., two colleagues going on a business trip together who travel to the air- port independently from their homes). These issues have to be addressed in the questionnaire wording (see Figure 5-1). Question DIA1999 MWCOG 2000 LAWA 2001 MTC 2001 Airline/flight Flight destination Originating/connecting Originating only Arriving/departing/connecting Final destination of air trip Purpose of trip Number of people in air travel party Number of well-wishers Departure time from trip origin Arrival time at airport Before flight Type of ground access trip origin Ground access trip origin address Mode of transportation to airport Use of parking/terminal curb Parking facility used Duration vehicle parked How accessed bus or train Reason for choosing access mode Number of checked bags Number of carry-on bags Where checked bags Use of airport in past year Use of other airports in area State of residence Country City/zip code of residence Nights away on trip/nights in area Time of arrival/return flight Airport used for arrival/return Egress mode on arrival/return Number of people in household Total annual household income Vehicles available at household Age of respondent Gender of respondent Satisfaction with facilities/services Amount spent while visiting area Amount spent at airport Reason for choosing airport Preferred airport Note: Table does not show all questions asked in each survey. Sources: DIA 1999 Denver International Airport, 1999 DIA Intercept Survey, Denver, Colorado, September 1999. MWCOG 2000 Metropolitan Washington Council of Governments, 2000 Washington–Baltimore Regional Air Passenger Survey, Washington, D.C., June 2002. LAWA 2001 Los Angeles World Airports, 2001 Air Passenger Survey, Los Angeles, California, April 2004. MTC 2001 Metropolitan Transportation Commission, 2001 Airline Passenger Survey, Oakland, California, September 2003. Table 5-1. Information obtained in a sample of air passenger surveys.

76 Guidebook for Conducting Airport User Surveys A related issue is the extension from air party travel patterns to vehicle trips, which are typically required for groundside and ground access planning. In some cases (e.g., use of rental cars or pri- vate vehicles parked at the airport for the duration of the air trip), there is usually a one-to-one correspondence between the air party trip and the associated vehicle trip. In other cases (e.g., pas- sengers dropped off at the airport by private vehicles), there will be two one-way vehicle trips for each one-way air party trip. In the case of taxis or hired limousines, there may be additional vehi- cle trips, depending on whether the operator is able to obtain a fare in the other direction. In the case of shared-ride modes, the number of air parties in each vehicle trip can vary widely, depend- ing on the ability of the operator to combine parties into a single trip. Therefore, for some modes it is useful to determine how many of the air party were in the vehicle that the survey respondent traveled in to the airport and how many other passengers (not from the air party) were also in the vehicle. Figure 5-1 shows some possible question wording to address this issue. The differences in air and ground access party composition and characteristics raise the ques- tion of whether to present survey results in terms of air parties, ground access parties, or air pas- sengers. Depending on how the results are going to be used, it may be desirable to present the results more than one way. From the perspective of ground access planning, it may be best to present results in terms of ground access party or air parties, because, generally, each air party represents a single ground access decision (with the caveats noted above). However, for shared- ride modes one may want to know what percentage of air passengers use the mode, because, gen- erally, ridership on such modes is counted as people rather than parties. The bottom line is that to interpret the survey results properly, it is important to understand the distinction and be clear what is being shown. Knowing the average air party size for each mode, the data can always be re-expressed on whatever basis makes the most sense for a given issue. Another issue that has to be addressed in planning an air passenger survey is the variation in passenger characteristics over the time of the day and days of the week. Typically a higher Including yourself, how many people are in your air travel party today? By air travel party, I mean all of the people who are traveling together with you on the same flight. If more than one person in air travel party, ask: And how many of these are children under the age of 18? If air travel party is more than six people, ask: Are you traveling as part of an organized group, such as a tour group, school party, sports team, etc.? Yes/No If Yes: What is the name of this group? _______________ (Ask following questions after asking about airport access mode used) If more than one person in air travel party, ask: Including yourself, how many of the people in your air travel party came to the airport together in the same vehicle as you? For shared-ride modes only (shared-ride van, courtesy shuttles, scheduled airport bus, charter bus or van), ask: How many other passengers (not including your air travel party or the driver) were in the vehicle when it arrived at the airport? Figure 5-1. Sample question wording to address travel party characteristics.

Air Passenger Surveys 77 proportion of business travel occurs at the start and end of the day and on weekdays rather than weekends, although a significant amount of originating business travel may occur on Sundays. The pattern of travel is also different for residents of the area and visitors: residents tend to leave earlier in the day, while visitors are more likely to travel later in the day. Example of Variation Over Day of Week and Time of Day To illustrate these effects, Figures 5-2 and 5-3 show the variation in the composition of air par- ties for two airports in the San Francisco Bay Area: Oakland International Airport (OAK) and San Francisco International Airport (SFO). The composition varies both by day of the week (Fig- ure 5-2) and time of day (Figure 5-3), although the variation is greatest by day of the week. There are also clear differences in traffic composition between the two airports. At OAK [Figure 5-2(a)], business travel accounts for the greatest proportion of the traffic on Wednesdays. The split between business travel by residents and visitors is quite different, with the highest proportion of resident business trips early in the week and the highest proportion of visitor business trips from the middle to the end of the week. Notably, busi- ness travel on Saturdays is not significantly different from Fridays. Personal travel shows the reverse pattern, with resident personal trips increasing toward the end of the week, with the highest proportion on Fridays. Visitor personal trips are at their highest proportion on Sundays and decline steadily during the week, reaching their lowest proportion on Thursdays and Fridays. The variation of traffic composition by day of the week at SFO [Figure 5-2(b)] shows a simi- lar pattern, although business travel remains strong through the end of the week, with the high- est proportion of visitor business trips on Fridays. The highest proportion of resident personal trips occurs on Thursdays rather than Fridays. The traffic composition by hour of the day at OAK [Figure 5-3(a)] appears fairly consistent until late afternoon, with the proportion of visitor personal trips increasing from about 4 p.m. (i.e., 16 on the 24-hour clock), reaching its highest level between 8 p.m. and 9 p.m. (20 and 21). The traffic composition at SFO [Figure 5-3(b)] shows somewhat greater variation by hour of the day, with a higher proportion of business trips in the early morning and from the middle of the afternoon until about 8 p.m. (20). The survey results for both airports appear to show an increase in the proportion of business trips between 11 p.m. and midnight (i.e., 23 and 24), although the small sample sizes at this hour make these proportions statistically unreliable. Unlike the situation at OAK, where the propor- tion of business trips made by residents is fairly consistent throughout the day, the proportion of business trips made by residents at SFO is highest in the early morning and declines progres- sively through the day. The traffic patterns at OAK and SFO illustrate the importance of ensuring adequate survey coverage for each day of the week and hour of the day. Performing a survey on only some days or during only some hours would bias the results. 5.2.2 Approaches to Surveying Air Passengers There are two very different approaches to performing air passenger surveys in airport ter- minals: intercept interview surveys, in which survey staff select potential respondents and record their answers to the survey questions, and self-completed surveys, in which question- naires are distributed to potential recipients to complete and return. The advantages and dis- advantages of each, together with some practical considerations, are discussed in the following paragraphs.

78 Guidebook for Conducting Airport User Surveys (a) Oakland International Airport 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Mon Tue Wed Thur Fri Sat Sun Day of Week Resident Business Resident Personal Visitor Business Visitor Personal (b) San Francisco International Airport 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Mon Tue Wed Thur Fri Sat Sun Day of Week Resident Business Resident Personal Visitor Business Visitor Personal Source: Metropolitan Transportation Commission, 2006 Airline Passenger Survey (Project team analysis of survey response data). Figure 5-2. Variation in air party composition by day of week—departing passengers.

(a) Oakland International Airport 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24+ Hour Resident Business Resident Personal Visitor Business Visitor Personal (b) San Francisco International Airport 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24+ Hour Resident Business Resident Personal Visitor Business Visitor Personal Source: Metropolitan Transportation Commission, 2006 Airline Passenger Survey (Project team analysis of survey response data). Figure 5-3. Variation in air party composition by hour of the day—departing air passengers.

Intercept Interview Surveys Intercept interview surveys are generally more costly to perform than self-completed surveys, because of the staff time required to perform the interviews. However, it is generally believed that the resulting data are of better quality, because the interviewers can ensure that questions are not skipped, clarify questions for the respondents, resolve ambiguous or unclear responses, and attempt to obtain responses to open-ended questions—such as the trip origin address—in the level of detail required. Interview surveys can also include more complex branching and follow- up questions, because the respondent does not generally see the questionnaire. The two principal planning issues with intercept interview surveys are as follows: • The protocol for selecting the potential respondents to approach and ask to participate in the survey. • Whether to use printed questionnaire forms or EDCDs. In the case of interviews in airline gate lounges, it is generally not feasible to interview every air party in the lounge, because of time and staffing constraints. Interviews can only take place over a limited period, typically 30 to 40 minutes, after enough passengers are in the lounge to provide a representative sample of air parties and before boarding commences. If the interview takes an average of five minutes, each interviewer would be able to complete six to eight inter- views. A typical domestic flight with a narrow-body aircraft might have 70 or more air parties (105 passengers) depending on the size of the aircraft and the load factor. At least 10 interview- ers would therefore be needed to survey every air party. Quite apart from the logistical difficulty of trying to conduct that many interviews simultaneously, passengers do not arrive in the gate lounge uniformly, so it would be necessary to interview a larger proportion of air parties closer to boarding time, further increasing the number of interviewers required. As a result, intercept interview surveys usually attempt to survey only a sample of air parties. In the foregoing example, a team of three interviewers might be able to survey every fourth air party. Interview surveys should define a sampling protocol that the survey staff will follow in order to avoid respondent selection bias. The following protocols are examples: • For an airline gate lounge interview with two interviewers, one interviewer should start with the right-most passenger (as viewed by the interviewer) seated in the row of seats furthest from the airline podium, then select every fifth passenger, counting to the left and proceeding around the rows of seats, from the outermost seats toward the center of the lounge. The sec- ond interviewer should start with the right-most passenger seated in the row of seats closest to the podium, then select every fifth passenger, also counting to the left and proceeding out- ward from the seats closest to the podium in a general counter-clockwise direction. • For a survey of passengers exiting security screening, the interviewer selects the next passen- ger to exit the screening area after completing each interview. The logic behind sampling every fifth passenger in the first example (when two interviewers might expect to survey about one-seventh of the passengers on the flight) is to allow for passen- gers who arrive after the surveying has started and sit in areas of the lounge that have already been surveyed, as well as those passengers that choose not to sit in the lounge at all. Because the layout of seating in airline gate lounges varies widely, sampling rules should be flexible enough to accommodate the different layouts that the interviewers are likely to encounter. Interpreting the sampling rules in different situations should be part of interviewer training. Examples of respondent sampling sequences in two different gate lounge layouts are shown in Figure 5-4. 80 Guidebook for Conducting Airport User Surveys

Air Passenger Surveys 81 Two issues arise in sampling passengers in an airline gate lounge. The first is that passengers will arrive in the lounge as the interviews are in progress. Some of these passengers will sit in areas of the lounge that have already been surveyed and therefore will be missed in the sampling process. Thus passengers who arrive in the lounge well before boarding commences will have a higher probability of being sampled than those arriving closer to boarding time. This occurrence needs to be considered in weighting the survey results. The second issue is that as the seating in the lounge fills up, some passengers may choose to stand. Members of large air parties, in particular, may not sit down, or some members of the group may stand while others sit. Passengers arriving in the lounge shortly before boarding is scheduled to commence may choose not to sit down, even if there are empty seats. Therefore, the sampling protocol needs to include standing passengers as well as those seated. Some passengers may also change seats or stand in a different part of the lounge as the inter- views are in progress. In particular, many passengers will get up and stand closer to the board- ing point as the time to board approaches. (One airline has formalized this process at some airports by installing numbered markers in the queuing area corresponding to a sequence num- ber on the boarding pass.) In principle, when passengers leave an area that has not yet been sur- veyed and move to an area that has been surveyed, or joins the queue waiting to board the flight, it is the same as if they arrived in the lounge at the time they changed positions. Podium 1 3 2 2 3 41 Interviewer 1 Interviewer 2 Podium 1 2 3 245 4 5 67 31 Interviewer 1 Interviewer 2 Figure 5-4. Typical respondent sampling sequences in airline gate lounges.

82 Guidebook for Conducting Airport User Surveys Obviously, there is a small chance that passengers who change position in the lounge could be sampled twice. However, interviewers will usually recognize people they have just interviewed, and passengers will generally indicate that they have already been surveyed if they were inter- viewed by another interviewer. The tradeoffs between the use of printed forms and EDCDs have been discussed in Section 4.9. For use in air passenger surveys, EDCDs have a number of attractive features. They can be pro- grammed to probe for detailed information on specific issues from certain respondents in a way that is transparent to the respondents and the interviewers. They can also be programmed to perform consistency checks on the response data and generate clarifying questions to resolve apparently inconsistent or implausible responses. Certain information, such as the time the sur- vey was performed, can be entered automatically. Information that repeats from one interview to the next, such as the location where the survey is being performed, can be entered once and then automatically recorded for subsequent interviews until the interviewer indicates that this has changed. Figure 5-5 provides examples of consistency checks that could be programmed into EDCDs, and Table 5-2 provides detailed follow-up questions that could be asked to resolve unclear responses or provide additional information. Another useful feature of EDCDs is the ability to vary the questions asked of different respon- dents. For example, a question that asks whether air passengers might have changed their ground access mode if a proposed new service had been available could vary the price or other attributes of the service in the wording of the question in order to explore how these factors affect the responses. The following consistency checks assume that EDCD programs can access relevant ground access service and other information. • Check that reported airline and flight number is reasonable for start time of interview and reported final destination of trip. • Check that reported parking facility and duration is reasonable for reported air trip duration and city of residence. • For reported use of ground transportation services with limited geographical availability (e.g., a shared-ride van operator serving only part of the region), check that reported trip origin is within service area. • For reported use of fixed-route ground transportation service from a given stop, check that the stop is a reasonable choice from reported trip origin. • For reported use of hotel/motel courtesy shuttle, check that reported trip origin hotel/motel offers courtesy shuttle service. • Check that number of air travel party members reported coming to airport in same ground access vehicle is not greater than reported size of air travel party. • Check that reported number of air travel party members coming to airport in same ground access vehicle is reasonable for reported vehicle. • Check that reported arrival time at airport is earlier than start time of interview by a reasonable amount. • Check that reported ground access time from trip origin to airport is reasonable for reported trip origin and ground access mode. • Check that reported number of checked bags is reasonable for reported size of air travel party. Figure 5-5. Sample consistency checks.

Air Passenger Surveys 83 Because the number of interviews that each interviewer can perform in a given period is fairly constant, there will be a higher sampling rate during periods when the flow of passengers is reduced or when the flights have fewer passengers. Therefore, staffing levels may need to be increased during busy periods or when surveying flights that use larger aircraft in order to achieve a fairly consistent sampling rate. Self-Completed Surveys Self-completed surveys should be conducted in a location where respondents are able to fill out the form, which limits the use of this approach to the airline gate lounge or similar location where passengers are seated and have time to do it. The advantage of self-completed surveys is Purpose Follow-up Questions Resolve Inconsistencies Just to confirm that I have this correct, you stated that you began your trip in (city) and boarded the (airport bus) at (stop). Did I record that correctly? Yes/No If Yes: Did you travel directly from your trip origin to the stop, or did you stop somewhere along the way for some other purpose? (Record location of intermediate stop, if applicable, using trip origin questions.) If No: Return to relevant question and revise response. Just to confirm that I have this correct, you stated that (number) of your air travel party came to the airport in the same vehicle. Did I record that correctly? Yes/No If No: Revise relevant response. Just to confirm that I have this correct, you stated that you began your trip in (city) at (time) and arrived at the airport at (time). Did I record that correctly? Yes/No If Yes: Did you travel directly from your trip origin to the airport, or did you stop somewhere along the way for some other purpose? (Record location of intermediate stop, if applicable, using trip origin questions.) If No: Return to relevant question and revise response. Just to confirm that I have this correct, you stated that you arrived at the airport (number) hours ago at (time). Did I record that correctly? Yes/No If No: Revise relevant response. Just to confirm that I have this correct, you stated that the (number) members of your air travel party checked a total of (number) bags. Did I record that correctly? Yes/No If No: Revise relevant response. Obtain Additional Information for Specific Access Modes Rental car Were any passengers dropped off at the curb in front of the terminal before returning the rental car? Yes/No. Scheduled airport bus At what stop did you begin your trip on the (airport bus)? (Check response option or write in.) How did you get to that (airport bus) stop? (Check response option or write in.) Rail system At what station did you begin your trip on (the train)? (Check response option or write in.) How did you get to that (train) station? (Check response option or write in.) Hotel/motel courtesy shuttle Did you stay overnight at that hotel, or did you visit the hotel only for the purpose of getting to the airport? (Check response option.) Did you park at that hotel, or did you get to the hotel some other way? (Check response option or write in.) Table 5-2. Representative follow-up questions.

that a large number of survey forms can be distributed and collected by one or two survey per- sonnel. A common procedure is to distribute the forms to passengers as they enter the gate lounge area and collect them as the passengers board the aircraft, although some passengers may hand the completed forms back before boarding commences. An important consideration is whether to attempt to survey passengers who arrive at the gate after boarding has begun. Excluding these passengers may bias the sample if those arriv- ing close to flight departure time have different characteristics from those arriving earlier. In general, passengers arriving at the gate once boarding has started will not have time to com- plete the form before boarding, and therefore if survey forms are to be distributed to these passengers they will need to be designed so that they can be completed later (e.g., on the flight) and returned by mail. In this case, it will be desirable to have a second staff member collect the forms as passengers board the aircraft, so that the person distributing the forms can continue to do so. The designers of the survey form need to consider that respondents may not have a flat sur- face to write on. Printing the forms on thin card with a three-part fold produces a form that is convenient to handle and sufficiently rigid to write on while holding in one hand. Survey staff should have an adequate supply of pencils or pens to give to respondents who do not have one. A number of issues arise with self-completed surveys that need to be carefully considered in the wording of the survey questions, design of the form, and analysis of the results: • It will not always be possible to determine which passengers are in the same air party when distributing the forms, so it is common practice to distribute forms to every adult passen- ger. In some air parties more than one passenger will provide responses, while other pas- sengers may decide not to complete the form if they see someone else in their air party doing so or complete it together. It will therefore be necessary to ask about the size of the air party and identify multiple responses from the same party before analyzing the results, so that these responses are not double-counted. Some surveys ask how many respondents from the air party have responded to the survey. However, experience has shown that these answers are often unreliable, possibly due to respondents misunderstanding the term “air party” or other members of their party starting to fill out the form but not finishing. Therefore, it may be safer to identify multiple responses on the basis of the information provided, as discussed further below, or use this question on multiple responses in conjunction with other infor- mation provided. • Respondents may not be familiar with local terminology, particularly for ground transporta- tion services. It is important to describe response options in terms that can be generally under- stood, rather than use the names of particular local services or facilities. Having respondents provide the name of the transportation provider, service or facility they used, where appropri- ate, can help resolve misunderstandings over terminology such as “airport bus” or “off-airport parking.” • Skip or branch patterns, when used, should be clearly shown on the survey form, with bold arrows directing the respondent to the next relevant question. Where questions only apply to some respondents (e.g., which parking lot was used), it is better to explicitly direct those respondents to the question with a branch from a previous question rather than ask the question in a way that requires each respondent to decide whether to answer it or not. • Check boxes for response options should not be too small or too close together. If the check boxes are too close together, it may be difficult to determine which one respondents intended to check. 84 Guidebook for Conducting Airport User Surveys

• Fonts used on the survey form for text that the respondent is expected to read should be no smaller than 10 point. Many respondents may have poor eyesight, particularly in the prevail- ing lighting conditions in a gate lounge area. To identify responses from the same air party in self-completed surveys, the analyst can make use of such information as the following: • Trip origin address (or other location information). • Final destination for air trip. • Home zip or postal code. • Air party size. • Air trip duration or duration of visit. • Departure time from trip origin. • Ground access mode used. While this process can be partly automated, there will be questionable cases where the ana- lyst will not be able to resolve whether two responses are from the same air party, and inspec- tion of the detailed response data will be necessary to make a decision. This process adds to the data-cleaning workload and constitutes one of the tradeoffs with the lower cost of self- completed surveys. One issue that arises with self-completed surveys is what to do if members of what is obviously the same party (e.g., they started from the same address and are on the same flight to the same destination) give conflicting information to other questions. This happens more often than might be expected. It may be naive to assume that every survey respondent understands the ques- tions and gives the correct answer. There is also the possibility that apparently conflicting answers are in fact correct—for example, different members of the same party may have differ- ent trip purposes or may be returning at different times—or that the apparent inconsistency is a coding error or the result of an unclear response. In cases where conflicting responses are unlikely to both be correct (e.g., passengers traveling on the same ground access vehicle giving different departure times from the same trip origin), it will be necessary to define a rule for which response to accept. In some cases, examining the responses to other questions may resolve the issue. For example, one departure time may be physically impossible, given the arrival time at the airport, or be an obvious error, such as record- ing the time as a.m. rather than p.m. It should also be borne in mind that for some questions (such as the time of departure from the trip origin) respondents will be giving their answer to the best of their recollection. Minor differences in answers from members of the same air party are to be expected. Hand-out/Mail-Back Surveys Because of the very low response rate that is typically experienced with mail-back surveys, this approach should only be used in situations when there is not enough time for the respondent to complete the survey and it is not practical to collect the completed survey forms later. Mail-back questionnaires should include a pre-paid return envelope. 5.2.3 Survey Locations The choice of location to perform an air passenger survey has significant implications for the logistics involved as well as the ability to obtain a representative sample of the target population. The principal options and the associated logistical constraints have been discussed in general terms in Section 2.8. This section discusses the advantages and disadvantages of the different options in meeting the objectives of an air passenger survey. Air Passenger Surveys 85

Non-Secure Locations Inside the Terminal Building. Within the terminal building there are typically two possi- ble non-secure areas for conducting interviews: one area for surveys of arriving passengers and one for departing passengers. The non-secure arrivals area of the terminal can be either open or enclosed; the former is typ- ical of smaller domestic operations and the latter is more usual at larger domestic or international operations. The domestic arrivals hall usually provides an opportunity to interview arriving air passengers with any greeters (if present) while waiting for baggage. (Note that passengers with- out checked baggage would not be included in such a survey process.) For international arrivals the greeters will typically be waiting—en masse—in front of the exit from the customs and immi- gration hall. While it may be possible to interview the greeters as they wait, it is not advisable to wait for the passengers to join them. The most suitable non-secure departures area is the lobby in front of the ticket and check-in counters. This area may or may not include other services, such as food concessions or conven- ience stores. Well-wishers could still be with the air passengers in this area, and members of the entire group can be interviewed. While the lobby is a possible survey location, it is not recom- mended for surveying air passengers and should only be considered as a way to obtain informa- tion from well-wishers. Although it is possible to perform an intercept survey of air passengers before they join the secu- rity screening line, passengers are usually anxious to complete the check-in and security screen- ing process and may be reluctant to take the time. Passengers may spend some time waiting in line, either for check-in or security screening, but this environment is not particularly good for interviews. The passengers need to move with the line, which interrupts their attention to the interview, and they are usually near other passengers, which may make them reluctant to answer some types of questions. During less busy periods, the line may be too short to complete the sur- vey before the passengers reach the check-in counter or screening location. Also, interviewing pas- sengers in the check-in lobby will miss any passengers who already have a boarding pass, which is becoming more common now with Internet and cell phone check-in, and are not checking bags. The best location to survey passengers before security is as they join the line for security screen- ing, because this line will include all passengers. If the line is fairly short, passengers may not mind being asked to step aside to complete the survey. It is advisable to determine their flight departure time to ensure that there is enough time for them to complete the survey without missing their flight. If the line is long, their willingness to participate may be increased if they can be offered the opportunity to go to the head of the line afterwards. This of course will require the agreement of the local Transportation Security Administration (TSA) staff, but it is fairly common when the security line is long to give passengers who may miss their flight priority in the line. The problem of potential bias from not surveying late-arriving passengers is no different from any other survey location, although it may involve a higher proportion of passengers, and can be addressed by having mail-back survey forms to distribute to such passengers. Groundside Locations. Intercept surveys of air passengers can also be performed in non- secure locations on the airport groundside, such as the terminal curb front, parking lots or pay- ment machines, transit stations or boarding areas, rental car facilities, and inter-terminal shuttle bus stops or people-mover stations. (Section 5.9 discusses groundside surveys in more detail.) With the exception of the terminal curb front, these locations will only allow a subset of air passengers to be surveyed. However, they may allow a larger sample of this subset to be obtained to supplement a more general sample of air passengers obtained at other locations. For exam- ple, the proportion of air passengers using transit is typically fairly small. Thus a survey in air- 86 Guidebook for Conducting Airport User Surveys

line gate lounges will obtain relatively few responses from passengers who used transit to access the airport. If the survey sponsor is particularly interested in collecting data on transit use, it would be helpful to obtain a larger sample of transit users by surveying passengers at transit stops or stations. If the survey sponsor wishes to obtain information on air passengers’ airport egress travel rather than their access travel, surveys could be conducted in the baggage claim areas, at the ter- minal curb front, or as passengers exit the secure area of the terminal. Such surveys need to be fairly short, because respondents will generally want to quickly complete their journey or may be anxious to meet some scheduled or pre-arranged ground transportation. A survey of passen- gers exiting the secure area of the terminal will intercept a sample of all arriving passengers, but some may not have made ground transportation arrangements and will be anxious to do so. Also, this is the point at which arriving passengers are often met by greeters, which is not an ideal situation in which to perform a survey. As with many aspects of conducting air passenger surveys, there is no ideal solution. The choice of location to survey arriving air passengers involves a tradeoff between the ability to sam- ple all arriving passengers, their willingness to be surveyed, and the extent to which respondents know how they will reach their final destination, as well as such considerations as whether there is adequate space to perform the survey without obstructing the flow of other passengers and how many locations can be staffed at a given time. Experience with airport user surveys shows that people are generally cooperative and may go out of their way to assist with the survey. This cooperativeness is no different in the non-secure area from the secure area, although the time that respondents may be willing to spend being interviewed will often be much less. Other Considerations. Interview Time. Intercepting airport users in the non-secure area is subject to a significant time constraint. Departing passengers may still have many steps to com- plete before boarding, including check-in, baggage drop, security screening, and perhaps shop- ping or obtaining a meal. It is therefore imperative that the survey be short. A good guideline is one single-sided form. If all the questions cannot fit into this space, the form is likely too long. It is possible to conduct a meaningful interview—obtaining many key characteristics of the air passengers, greeters, and well-wishers traveling in a group—in under one minute, although this is highly dependent on the skill of the interviewer. A maximum interview time of two minutes is recommended. For longer surveys, alternative locations on the secure side of the terminal—or different methods, such as mail-back forms— should be considered. Security Clearance. In the current security-conscious environment, an airport is viewed as a relatively vulnerable location and personnel with access to the secure side of the terminal must undergo security clearance and be issued identification badges. Conducting a survey on the non-secure side may remove some of this constraint, depending on the particular requirements of the airport. Even so, it may be worthwhile to issue survey field staff with identification badges and authorization letters in case they are challenged on their right to conduct the survey and to reassure potential respondents that this activity is officially sanctioned. After Security Screening An alternative approach is to intercept passengers as they exit security screening. This approach has the advantage that air parties are generally still together and the survey will inter- cept all passengers clearing security, whether they go directly to their gate or not. Passengers who do not go to their gate until the flight boarding time have an equal chance of being included in Air Passenger Surveys 87

the sample as those that spend the time before the flight waiting in the gate lounge. Intercepting passengers as they exit security screening also samples passengers on all flights departing from the gates served by the security screening channels, not just those on flights from selected gates. However, surveying passengers as they exit security screening is only suitable where informa- tion is not being collected on connecting passengers. Most connecting passengers do not pass through security unless they are changing terminals, and the characteristics of the small number of connecting passengers that do go through security will likely be very different from those of other connecting passengers. There are two other potential disadvantages with this location: • Passengers with limited time before their flight is due to depart may be anxious to reach their gate. The airlines may also be concerned that the survey will delay passengers. • There is often no seating in this area, so the interview may have to be conducted with the pas- sengers standing. The first issue can be addressed by asking the passengers what time they were told to be at the gate for boarding and the gate number (for large terminals). This information is usually printed on their boarding pass. Asking to see their boarding pass in this context is a non-intrusive way of verifying their flight number. If there is insufficient time to conduct the survey, the interview- ers can ask if they can accompany the passengers to the gate and perform the interview there. Generally there will be enough time to complete the survey in the gate area while other passen- gers are boarding. If passengers appear elderly or uncomfortable standing for the interview, the interviewers can ask if they would like to go to a nearby gate area to be interviewed, so that they can sit down. Alternatively, it may be possible for the airport to provide some temporary seating in the area where the survey is being performed. Because surveying passengers as they exit security screening will obtain a sample of all origi- nating passengers departing on flights from the gates served by that security checkpoint, it will be necessary to weight the results to reflect the total number of originating passengers on those flights. Passengers should be asked if they are connecting between flights so that they can be excluded from the weighting of responses in the analysis. Because the sampling rate will vary with the flow through the security checkpoint, and because the interview rate will be relatively con- stant for a given staffing level, it will be necessary for the weight assigned to a given response to reflect this varying sampling rate. If possible, passenger throughput counts should be obtained from the TSA in 10- or 15-minute intervals to allow for short-term fluctuation. Where these counts are not available, it will be necessary to assign a survey staff member to count passengers exiting security or estimate the flow from the flight schedule and the estimated passenger load on each flight. The distribution of the time before scheduled flight departure that passengers on a particular flight clear security can be estimated from the survey results and then applied to the estimated passenger loads to estimate the flow rate through security, with appro- priate adjustments for passengers on connecting and through flights. Airline Gate Lounges One of the most common locations for an air passenger survey is the airline gate lounges. Pas- sengers in the lounges are generally seated and are usually willing to participate in a survey. They tend to remain in the same seats and the seats are typically grouped in rows, which in the case of an interview survey facilitates a consistent approach to selecting passengers to survey. However, there are a number of disadvantages to performing a survey in this location and some aspects that need careful planning. The most obvious consideration is that passengers in a 88 Guidebook for Conducting Airport User Surveys

given gate lounge are generally waiting for the next flight to depart from that gate, and thus are all traveling to the same destination airport, although this may not be their final destination if it is an airline hub or international gateway. There must therefore be careful selection of flights to survey in order to obtain a representative sample of air passengers in all markets. Some passengers in the lounge may be waiting for a later flight or for a flight from a nearby gate. Should such passengers be included in the sample? On the one hand, including these pas- sengers in the survey may result in obtaining fewer responses from the other passengers than anticipated in the flight sampling plan. On the other hand, including them may provide survey responses from a broader sample of flights than those included in the flight sampling plan, which could be regarded as a good thing. In cases where the survey is attempting to obtain responses from every adult passenger on a flight, including a few responses from passengers on other flights may unduly complicate the response weighting process or lead to biased results. It may be preferable to ask passengers which flight they are taking when handing out the survey forms and only survey those on the sampled flight (or only code those responses from passengers on the sampled flight). However, with interview surveys, responses will be obtained from a relatively small sample of passengers on the sampled flight anyway, because of time and staffing constraints. Use of weight- ing factors which expand the responses to reflect the passenger traffic in fairly broad groups of markets, by time of day and day of the week, will generally be preferred to factoring up the few responses from a flight to the estimated passenger load for that flight. This approach avoids potential bias from over-weighting survey responses from flights for which a smaller proportion of air parties were interviewed. A major disadvantage of performing an interview survey in airline gate lounges is the small opportunity that interviewers will have to survey passengers who arrive at the gate just before or after boarding begins. If those arriving at the gate close to flight departure time have different char- acteristics from those arriving much earlier, as is quite likely, the survey will give biased results for those characteristics. This bias can partly be addressed by providing such passengers with a mail- back survey and through the process of weighting survey responses, discussed in Section 5.5. Another practical difficulty with airline gate lounge surveys arises from the limited time win- dow for any given flight during which passengers can be surveyed. If interviews are started too soon, there will be nobody in the lounge to survey. Once boarding has commenced, it will gen- erally be difficult to get passengers to agree to participate. This time window will generally begin about an hour before the scheduled flight departure time and end when boarding starts, which is typically 20 to 30 minutes before flight departure. In the case of flights using wide-body air- craft, passengers will often begin arriving in the gate area somewhat earlier, and there will usu- ally be enough passengers in the lounge to begin interviewing an hour and a half before the scheduled flight departure time. However, boarding often begins as much as 40 minutes before flight departure. Some international flights start boarding as much as 60 minutes before flight departure and there may be enough passengers in the gate lounge two hours before departure to allow interviews to begin. Once a survey team has finished surveying a particular flight, it will need to move to the next flight to be surveyed, unless the team is scheduled to take a break. The next flight should therefore have a scheduled departure time at least an hour later (an hour and a half in the case of a wide-body aircraft and two hours for international wide-body flights). This requirement lim- its the flight sampling plan, because there may be few flights departing around that time. If those that are departing around that time are leaving from gates some distance away, additional time will be required for the survey team to travel between gates, particularly if this travel involves going through security screening again. As discussed in more detail in Section 5.3, developing Air Passenger Surveys 89

a flight sampling plan that provides reasonable coverage of different flight destinations and airlines—while utilizing survey teams efficiently and allowing staff to take required breaks at appropriate intervals—is a major challenge. 5.3 Sample Size, Survey Coverage, and Timing Once the details of the survey methodology have been determined, the next steps are to decide on the required sample size, develop a sampling plan to provide adequate coverage of the varia- tion in air passenger characteristics over time, and decide when to perform the survey. 5.3.1 Sample Size The details of calculating sample sizes for different sampling methods are discussed in Section 3.4. In air passenger surveys, the most common type of sampling method uses cluster sampling to select a random sample of flights as clusters and then attempts to survey either all the passengers on each selected flight (with a self-completed survey) or a sequential sample of passengers on each flight (with an interview survey). The accuracy of a cluster sample depends on both the variance of the characteristic of interest within each cluster and the variance between clusters. Where each cluster is a flight, whether the mean of a given characteristic varies significantly between flights will depend on the characteristic. However, many characteristics—such as airfares, ground access mode use, air trip duration, and air travel party size—are likely to vary significantly by destina- tion and hence their sample mean will vary between different flights. Of course, these character- istics vary widely within a given flight as well. Therefore, it will generally be necessary to use a significantly larger sample size with flight-based cluster sampling than with random or sequen- tial sampling of the air passenger population in order to achieve a similar level of accuracy. As a practical matter, the only way to perform random or sequential sampling of the air pas- senger population without resorting to a flight-based cluster sample is to interview passengers at a location where all passengers can be intercepted, such as the exit from security screening. The extent to which a flight-based cluster sample should increase the sample size to provide an equivalent level of accuracy to that calculated for a random sample is dependent on the spe- cific traffic composition at each airport, the characteristics of interest, and how these vary between passengers on particular flights and on average between flights. This issue is not at all well understood and is deserving of further research. In the absence of more specific analysis, it would be prudent to increase the sample size by a factor of two for well-designed interview sur- veys of air parties, with appropriate stratification of flights16 and approximately 20 air passengers interviewed on average per flight. This factor increases as the number of passengers interviewed per flight increases. In the above case, a factor of 1.5 would be more appropriate where an aver- age of 10 passengers per flight is interviewed, but a factor of 6 would be more appropriate where an average of 90 passengers per flight is interviewed. Sample size with cluster sampling is dis- cussed in more detail in Appendix B. 5.3.2 Estimating the Population of Airport Users on a Given Day To develop a sampling plan for a given day, it is desirable to have an estimate of the number of air passengers (and possibly the associated greeters and well-wishers) using the airport on that day. If the sampling plan is being developed a fairly short time before the survey, it may be pos- 90 Guidebook for Conducting Airport User Surveys 16 Assuming an intra-class correlation coefficient of 0.05.

sible to obtain expected passenger loads on each flight from the airlines. If the sampling plan is being prepared well before the start of data collection or the airlines are not willing to provide this information, the population of these categories of airport users per day can be estimated as follows: • Passengers—Obtain a schedule of departing flights (and arriving flights if interviewing arriv- ing passengers) for the survey period from the airport operator or sources such as the Official Airline Guide (OAG). The schedule should indicate the flight departure (or arrival) time, air- line, flight destination (or origin), terminal, aircraft type and seats, and whether it is a through flight or originating (or terminating) at the airport. This information can be determined from the full flight itinerary or routing. For each flight, estimate the load factor using past data for the airline and city pair.17 This estimate could be further refined, if necessary, to allow for variation in load factor by month, day of week, and time of day where data for this level of detail is available.18 For through flights, estimate the proportion of passengers who will continue on the flight and not leave the aircraft.19 The proportion will vary by routing, airline, and airport and may need to be estimated based on limited qualitative inputs (e.g., comments by gate staff or other knowledgeable people). Multiply the seats, load factor, and proportion of passengers not continuing on the flight to estimate the enplaning (or deplan- ing) passengers. The daily or hourly passengers are then found by summing the estimated passengers over the flights in that time period. Connecting passengers do not make use of the groundside facilities or transportation system and can be excluded, where necessary, by multiplying by the ratio of origin/destination (O/D) passengers to enplaned/deplaned pas- sengers for that airport. This approach can be extended to estimate the proportion of the passenger population in different market segments (e.g., domestic versus international pas- sengers, or passengers using a specific terminal), based on the flight destination (or origin in the case of arriving flights). • Greeters and well-wishers—Numbers vary greatly with airport size, types of service available, proportions of business and visiting (non-local) passengers, and public transportation ser- vices to the airport, among other factors. The numbers of well-wishers and greeters that come into the terminal can be estimated based on the numbers of O/D passengers. While these vary significantly by airport, month, day of week, and time of day, a rough guide to the average number of well-wishers per originating passenger based on recent airport surveys is shown in Table 5-3. The number of well-wishers can be estimated by multiplying the number of originating pas- sengers by an appropriate factor based on the data in Table 5-3. Note that many of these well- wishers will be in groups and may be seeing off several passengers. Numbers of greeters are typically similar to the numbers of well-wishers. 5.3.3 Sampling Strategy The design of the sampling strategy is key to obtaining reliable results in an air passenger sur- vey. A poorly designed sampling strategy can exclude certain subgroups from the sample entirely and lead to biased results. As discussed in Section 3.3, a controlled sample attempts to design the sampling strategy so that the composition of the sample reflects the underlying distribution of the population characteristics fairly accurately. In the case of air passenger surveys, this means Air Passenger Surveys 91 17 Monthly data on passenger loads by airline and flight segment are available from the U.S. Department of Transporta- tion Bureau of Transportation Statistics T-100 database. 18 Some airports require airlines to report passenger loads by flight. 19 The difference between arriving/departing and enplaned/deplaned passengers.

that the sample has the same (or very similar) proportions as the population for such character- istics as the following: • Airline. • Flight departure time. • Day of the week. • Destination. • Originating versus connecting traffic. • Domestic versus international trips. In practice this is very difficult to achieve. Each of these characteristics varies independently of the others, resulting in a huge number of potential combinations of characteristics, and the logistics of performing the survey limit the ability to vary the sampling rate to match the underlying distribution of characteristics. In particular, intercept interview surveys tend to under-sample during busy periods and over-sample during less busy periods, because it is difficult to schedule the number of interviewers to match the changes in passenger flow. When the sample is not controlled to ensure that the composition of the sample corresponds to that of the population, the results of the survey can be weighted so that the reported results reflect the composition of the population rather than that of the sample. The process for deter- mining the weights to be used is discussed in Section 3.5. Sampling Passengers The first consideration in sampling air passengers is to decide whether to sample individual pas- sengers or air travel parties. As discussed earlier in this chapter, this decision is largely a function of the survey method adopted. Self-completed survey forms are typically distributed to every adult passenger in the group of interest, while intercept interview surveys are usually designed to collect information on air parties. There is obviously no difference in the case of one-person parties. The objective in defining a sampling strategy to survey air passengers is to obtain a random sample of respondents. Where the flow of passengers or the sequence of passengers in a queue is already random with respect to the characteristics of interest, selecting every nth passenger will generate a random sample of respondents. When a respondent is in an air travel party of more than one person, the count to determine the next nth passenger in a sequential sampling strat- egy should start again if the next nth passenger is a member of the air party that has just been interviewed. This method will avoid interviewing multiple passengers from the same air party. Members of the same air party will typically be standing or seated together, and it will usually be 92 Guidebook for Conducting Airport User Surveys Table 5-3. Representative ratios of well-wishers to originating passengers. Airport Size Terminal Type Airport Year Well-wishers per Originating Passenger Large hub International New York JFK Terminal 4 2003 0.29 International San Francisco, California 2006 0.17 Domestic San Francisco, California 2006 0.14 Medium hub Domestic San Jose, California 2003 0.16 Domestic Oakland, California 2006 0.18 Domestic Winnipeg, Manitoba 2007 0.25 Small hub Domestic Birmingham, Alabama 2005 0.09 Domestic Quebec City, Quebec 2006 0.19 Domestic Victoria, British Columbia 2006 0.35 Source: Airport surveys conducted by Jacobs Consultancy

obvious who is in the party. Where it is not obvious, it may be necessary for the interviewer to ask the respondent who has just been interviewed to indicate the members of the air party. In the case of large air parties, such as tour groups, members of the party may not remain together in the terminal, and thus the sampling strategy may happen to interview several members of the same party. Large air parties call for particular consideration in analyzing survey results, as dis- cussed in Section 5.2.1, to account for the possibility that the survey may interview several mem- bers of the same party or that different members of the party may have traveled to the airport separately. With large air parties (more than about six people), it may be helpful to record the name of the group organizing the trip in order to identify other respondents from the same group when analyzing the results. Where passengers are moving, such as at an exit from security screening or an entrance to the terminal building, the duration of each interview will generally be sufficiently long that by the time the interview is completed, the next passenger in the stream will be effectively chosen at random. Also the variation in the duration of each interview will help ensure the randomness of the sample. Where passengers are grouped by some characteristic, such as passengers in a check-in queue at an airline counter, the sampling strategy should attempt to distribute the interviews across the different groups in proportion to the passengers in each group, such as the number checking in on each airline. However, this is difficult to achieve in practice, particularly because those pas- sengers in short queues may not be in the queue long enough to complete an interview. For these reasons, queues are generally not a good location to perform intercept interview surveys. In locations where passengers are not in an ordered sequence, such as in airline gate lounges or baggage claim areas, it will be necessary to define a starting point for the sequence of passengers in the sample and a rule for the direction to move to determine the next pas- senger to interview. One such rule for airline gate lounges was suggested in Section 5.2.2. A similar rule for baggage claim areas might be: Start with the person standing closest to the airline baggage office door, then select every sixth person, proceeding clockwise around the baggage claim device. The exact starting point is not particularly important, and interviewers can use their judgment as to which person is closest to a defined point in ambiguous cases. The point is to ensure that the interviewers follow a defined rule to select the passengers to interview rather than selecting them on the basis of whether they appear likely to be cooperative or some other criterion that might bias the sample. Similarly, the interval between sampled passengers is not particularly crit- ical. The objective is to ensure that interviews take place throughout the area in question and so should be chosen in the light of the number of interviews anticipated to be performed and the number of passengers expected to be present in the area. In the case of baggage claim areas, allowance should be made for greeters waiting with the passengers. When there is more than one interviewer performing interviews in a given area, the sampling rule will need to ensure that they each start at a different location and the sequences of selected passengers do not overlap. Because the number of interviews that can be performed while the passengers are present in an airline gate lounge or baggage claim area is fairly limited, overlap is not usually a problem. For example, if each interview takes an average of four minutes and the passengers in a gate lounge are surveyed over a 40-minute period, each interviewer will only be able to complete 10 interviews. One issue that arises with airline gate lounge surveys is that the seats may all be taken before boarding of the flight begins and thus passengers arriving after this point will either stand in the gate area or find a seat in nearby lounges. A sampling protocol that includes only passengers seated in the gate lounge will systematically exclude passengers arriving close to flight departure Air Passenger Surveys 93

time. It may therefore be desirable to modify the sampling rule to include standing passengers when most of the seats are taken. In practice, where passengers sit (or stand) in a gate lounge or stand in a baggage claim area may be influenced by characteristics such as the time they reach the gate lounge or the order in which they arrive at the baggage claim device (which is influenced by the order in which they deplane and their walking speed through the terminal). However, as long as the sam- pling protocol includes all occupants of the gate lounge or claim area and samples people in proportion to the number occupying each part of the area, these differences will be reflected in the resulting sample. Sampling Flights In the case of airline gate lounge surveys, whether interview or self-completed, it is necessary to select a sample of flights to survey. This selection is a particularly challenging problem, because of the need to ensure appropriate coverage of airlines, destinations, and times of day, while utilizing the survey personnel efficiently. Flights depart at irregular intervals throughout the day. There will be periods when a large number of flights will depart around the same time and periods with relatively few (or even no) flight departures. To complicate matters further, different airlines serving the same market will often have their flights depart around the same time, partly for competitive reasons and partly due to time zone differences. Although the characteristics of passengers on different airlines in the same market may not necessarily be significantly different, this is not always the case. Factors that can cause passenger characteristics to vary by airline include the following: • Nationality of airline (flag of carrier) in international markets. • Type of carrier: low-fare versus network. • Market share and flight frequency. • If the destination is a hub for one of the airlines. • Flight departure times. Business travelers will tend to favor airlines that provide flight departures that better match the business day and those that offer higher frequency in case their travel plans change, while leisure travelers may be more willing to use flights at less convenient times and with fewer alternative departure times in order to obtain a lower fare. Passengers who are residents of cities that are airline hubs are more likely to be in the frequent flier program of the hub air- line, while residents of spoke cities are more likely to be in the frequent flier program of another airline, particularly if that airline has a stronger presence in the spoke city. Therefore, a fully stratified sampling plan would group flights by the following: • Airline. • Destination (possibly grouped by region). • Time of day. In practice, at many airports this approach would generate a very large number of separate groups, and it would be impossible to develop a viable sampling plan by selecting a sample of flights from each combination of these factors. Instead, the usual approach is to define a sam- pling strategy that ensures that the selected flights provide a reasonable sample of each of these three factors. One such approach is to list flights throughout the period of the survey in order of scheduled flight departure time and calculate the cumulative number of departing seats for each flight. If information on average load factor by market and time of day is known at the level of individ- ual flights, then the cumulative number of expected passengers can be calculated in place of seats. 94 Guidebook for Conducting Airport User Surveys

Flights are then selected by finding every mth seat in the cumulative seat count, where m is the ratio of the total number of seats to the number of flights to be sampled, considering the expected number of completed interviews per sampled flight. This process ensures that larger aircraft have a higher chance of being selected than smaller aircraft, which offsets the smaller likelihood of a passenger on a large aircraft being interviewed if approximately the same number of interviews is performed for each sampled flight. If more interviews are performed for flights using larger aircraft, as could occur if more inter- viewers are assigned to those flights or more time is available for the interviews, or if all adult passengers are sampled using self-completed survey forms, then either the flight sampling process needs to be modified or the results weighted accordingly. Where all or a constant pro- portion of passengers are sampled, the procedure is simpler. After arranging all flights in order of scheduled departure time, select every mth flight where m is the ratio of total flights to the number of flights to be surveyed. The latter is calculated by the total number of passengers to be surveyed divided by the average passengers per flight times the proportion of passengers on each flight to be sampled. If the survey will only be conducted for certain periods each day, the cumulative list of seats is only determined for flights scheduled to depart during the times when the survey will be per- formed. After identifying an initial list of flights to sample, the characteristics of those flights in terms of the above criteria can be compared to the corresponding proportions across all flights, and any necessary adjustments made to the sample by dropping some of the flights with char- acteristics that are over-sampled and replacing each of them with the next flight in the list of flights with the characteristics that are under-sampled. Further adjustments may be necessary to ensure that the survey field teams have a fairly steady workload throughout their shift. A flight that has a scheduled departure time too close to that of other flights in the sample could be dropped and replaced with another flight with the same characteristics but a scheduled depar- ture time during a period when the number of selected flights is not enough to keep the survey field teams occupied. 5.3.4 Survey Timing At most airports, air passenger characteristics vary seasonally and it is therefore important to determine whether information on these characteristics are required for a specific period (e.g., the peak month) or on an annual basis. If information on air passenger characteristics is required on an annual basis, it will be necessary to perform the survey in two or more periods, reflecting the seasonal pattern of traffic. Depending on the information of interest, it would be desirable to select a peak and off-peak period that represent the highest and lowest levels of the relevant characteristics (e.g., private vehicle trips to and from the airport, or proportion of business travel). This method should allow the corresponding characteristics to be estimated for other months that are not surveyed, although this may not always be possible, depending on how the different characteristics vary during the year. The survey planning team may need to undertake some analysis of monthly variation in those characteristics in order to select appropriate months for the survey. Where seasonal variation in travel characteristics is more complex than can be expressed in terms of peak and off-peak conditions (e.g., winter travel patterns are very differ- ent from summer travel patterns as well as from travel patterns in the spring and fall), it may be necessary to divide the survey into three or four phases or conduct the surveys continuously throughout the year. In addition to seasonal variation, at almost all airports air passenger characteristics vary by time of day and day of the week. This variation can be addressed by ensuring that the survey pro- vides reasonable coverage of different times of day and days of the week. Ideally, the survey data Air Passenger Surveys 95

collection would take place throughout the day for at least a full week. At many airports, passen- gers begin arriving for early morning flights by 5 a.m. and the last flight does not depart until midnight or later; therefore, the survey would need to cover about a 19-hour day. However, the staffing levels required to achieve this coverage are often impractical, and spreading the desired sample size across every time period may unduly constrain the sampling in each period. There- fore, it is common to survey for a limited period each day (typically at least eight hours) but vary the timing of these periods from day to day. Where traffic peaks occur at certain times on par- ticular days (e.g., Monday morning and Friday and Sunday evenings), the survey shifts should be scheduled to provide coverage for these periods. While some flights may depart early in the morning or late in the evening, typically these are fairly few and the sampling strategy should reflect the relatively small proportion of passengers at these times. It may be adequate to have only one or two survey staff during these times and only survey on a few days. However, at airports with international service, departures for certain markets may take place late at night because of time zone differences or to allow early morning arrivals at the destination. Similarly, some eastbound flights from the West Coast depart late at night in order to arrive at mid-continent hubs or East Coast destinations early the next morn- ing. This may require additional survey staffing at these times to make sure that those markets are adequately surveyed. At other times of day, there may be very few departures for periods of several hours at a time. Such flight schedules can present a challenge to survey staffing, because in general staff will want to work a full shift. It may be possible to schedule staff so that meal breaks occur during periods of low activity, although there are constraints on how long staff can work between breaks, and obviously meal breaks need to occur around the middle of the shift. With careful scheduling, it may be possible to provide increased staffing levels during busy periods by scheduling shifts to overlap during these periods. Figures 5-6 and 5-7 illustrate how traffic levels and the composition of the traffic can vary over the day or the days of the week. The figures show the distribution of departing seats from Logan International Airport in Boston for different markets for the week of the Thanksgiving holiday 96 Guidebook for Conducting Airport User Surveys 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5 10 11 12 13 14 15 16 17 18 19 20 21 22 Hour of Day D ep ar tin g Se at s Canada Cen.Am & Caribb Europe US < 500 miles US 500-999 miles US 1,000+ miles Source: Official Airline Guide for November 19, 2007 (excluding flights to Africa, 185 seats Tuesday and Friday). 6 7 8 9 Figure 5-6. Numbers of departing seats from Boston Logan International Airport by time of day and destination region.

in 2007. The traffic level varies widely over the day, with early morning and late afternoon/ evening peaks and a sharp drop in long-haul domestic departures (stage length of 1,000 miles or more) between 12:00 and 1:00 p.m. (12 and 13). Very few flights depart after 9:00 p.m. (21), most of them to Europe. As shown in Figure 5-6, departures for different international markets vary considerable through the day, with those to Central America and the Caribbean in the morning and those to Europe mostly in the evening. To adequately represent these markets in the sample, the sampling plan would need to ensure that the flights selected to be surveyed at those times include an appro- priate number of international flights. Figure 5-7 shows a reduction in the number of flights on the Thursday of the Thanksgiving holiday, with the number of flights gradually returning to nor- mal levels over the subsequent days. One approach to ensuring that the survey responses are appropriately distributed by time of day is to schedule interviewers so that the distribution of total interviewer time by time of day and day of week is similar to that of the departing seat capacity of the airport. For smaller total sample sizes (e.g., under 1,000 responses), interviewers are assigned to cover a larger number of flights by sampling only a small number of passengers from each flight (e.g., four to twelve depending of the size of the aircraft). Because connecting passengers tend to arrive in airline gate lounges earlier than originating passengers, starting to survey flights too long before flight depar- ture time will tend to over-sample connecting passengers. The interviews for a given flight should generally start no earlier than an hour before flight departure (90 minutes in the case of interna- tional flights) and be evenly distributed up to the time that boarding begins. This approach can work well at small to medium-sized airports. At larger airports, interviewer times would be deter- mined for each terminal in proportion to the numbers of passengers or departing seats from those terminals. Responses are then weighted to match departing passengers by time of day, flight destination, and airline using flight schedules and estimated load factors. As a practical matter it is difficult to schedule interviewers efficiently and match the inter- viewer time to the variation in departing seats on a daily basis. Instead, an attempt can be made to match interviewer time to departing seats in each hour separately for weekdays in total and weekend days in total. The start times and lengths of shifts and break times can be varied so there Air Passenger Surveys 97 0 10,000 20,000 30,000 40,000 50,000 60,000 Monday Tuesday Wednesday Thursday Friday Saturday Sunday Day of Week D ep ar tin g Se at s Thanksgiving Holiday Source: Official Airline Guide for November 19, 2007 (excluding flights to Africa, 185 seats Tuesday and Friday). Canada Cen.Am & Caribb Europe US < 500 miles US 500-999 miles US 1,000+ miles Figure 5-7. Numbers of departing seats from Boston Logan International Airport by day of week and destination region.

is more coverage in the peak periods, with interviewers typically working between four and eight hours per shift. Scheduling interviewers to match the distribution of departing seats (or passengers) has both staffing and cost implications. Having interviewers work for varying times per day and starting their shifts at different times can be done, but it may be necessary to pay more for people to work short shifts on some days or the earliest and latest shifts. Field supervision also becomes signifi- cantly more complicated with interviewers starting their shifts at different times. These factors need to be considered carefully in survey planning. 5.4 Questionnaire Wording and Length The general principles for questionnaire design and length are discussed in Section 4.3, and a sample passenger questionnaire is provided in Appendix F. The sequence and wording of sur- vey questions can significantly affect the reliability of the responses that are obtained, if respon- dents misunderstand a question being asked. Examples of problems that can arise include the following: • Terminology for ground access modes, particularly modes such as scheduled airport bus, lim- ousine, hotel courtesy shuttle, and charter van. In some areas, the term “limousine” is used for scheduled airport bus service and may appear in the name of the service, while a vehicle hired for the exclusive use of an air party may be referred to as a “hire car.” However, some respondents may confuse hire car with rental car. The term “shuttle” is often used to refer to shared-ride van service (and again sometimes appears in the name of the operator). An air party taking a shared-ride van service from a hotel to the airport may consider this a “hotel courtesy shuttle,” although that is not what is intended by the term. The distinction between shared-ride van service and charter van may be a matter of whether the operator is licensed to carry multiple travel parties in a single trip, which may not be known to the travelers, partic- ularly if the trip to the airport was arranged by someone else. • Trip purpose. Questions should generally provide more options than just business and per- sonal. The term “leisure” would usually be considered to exclude a wide range of personal trip purposes (e.g., attending a funeral) and should be avoided. Response options should allow for trips that combine business and personal purposes, such as combining a business meeting or conference with vacation time or leisure activities, or visiting family or friends. Asking the “main purpose” or “primary purpose” of the trip may be meaningless in cases where the trip only occurred because it allowed multiple purposes to be satisfied. The key issue to consider is why information on trip purpose is needed. If trip purpose is sought to distinguish between trips where the respondent is paying the travel costs and those where the costs are paid by their employer or other organization, it may be better to ask this ques- tion directly rather than assume that respondents reporting business trips are not paying for their travel costs themselves. • Trip origin. Typically the response sought is the origin of the ground access trip to the airport where the survey is being performed. However, if not carefully worded this question could be misunderstood by visitors as the origin of their entire trip from their home region. The expres- sion “your trip to the airport today” is ambiguous to travelers making a one-day return trip. In some cases, even the term “this airport” can be ambiguous. In a recent survey, respondents were asked to state the final destination airport of the air trip that they were about to begin. This was followed by a question that asked: “Is this airport the home end of your trip?” The second question was intended to mean the airport where the survey was being performed, but could easily have been misunderstood to mean the destination airport referred to in the pre- vious question. 98 Guidebook for Conducting Airport User Surveys

• Air party. This term may not be understood by many respondents and needs to be expressed in other words (e.g., traveling together on the same flight). For ground transportation plan- ning purposes it may be desirable to distinguish between the air travel party and the ground access travel party, because different members of the air travel party may have come to the air- port separately. 5.4.1 Trip Origin Information Sponsors of air passenger surveys often wish to obtain information on the ground access trip origin location (or ground egress trip destination location). This information is typically needed at a fairly detailed level to permit the trip origins or destinations to be coded to the sys- tem of transportation analysis zones used by the local regional transportation planning agency. This coding will allow information on highway and transit travel times and transit fares to be readily obtained from the data files maintained for regional transportation modeling. It will also allow the results of the air passenger survey to be integrated with other transportation planning studies. It is not uncommon for these zones to be significantly smaller than zip codes or postal codes. The usual approach is to request the street address and city of the trip origin. For obvious reasons, many survey respondents are reluctant to provide the actual address, although they may be willing to provide the block number or a nearby street intersection, which is sufficiently accurate. However, visitors to the area may have started or ended their access or egress trip at a hotel, business, or other discrete location (such as cruise ship terminal or convention center) for which they do not know the address. In such situations respondents should be asked to provide the name of the hotel or other location, and these will have to be coded later so that the correct address can be assigned to the survey response. In such cases, the trip origin or destination city should also be obtained, to resolve situations in which there are several locations with similar or identical names. Hotel names can be particularly problematical. In a large city there may be sev- eral hotels in the same chain, and while they will typically each have a unique name, respondents may not use the formal names but simply refer to them by the name of the chain. A related prob- lem can arise when ownership of a hotel has recently changed. Respondents who previously stayed in the hotel before the change may refer to it by its former name. Because respondents— visitors in particular—may give partial or even incorrect names for hotels and other locations, it will be helpful to also obtain a nearby street intersection or the name of the street if this is known. While this may be redundant information in many cases, it can be invaluable in resolv- ing ambiguous or unclear responses. In the case of printed questionnaires it will be necessary to obtain the redundant information from all respondents, because it would be too complicated to explain which respondents should provide it and which not. However, in the case of surveys using EDCDs, it may be possible to program the devices so that the street name or intersection question is skipped for responses that give location names that are clearly unambiguous. The issue of the ground egress trip destination is often ignored and it is implicitly assumed that the ground access trip and egress trip are symmetrical. However, this is not always the case, and this may deserve explicit attention in the survey. In particular, situations where they are not the same may be an important factor in access and egress mode choice. Common examples include visitors who travel from the airport to a hotel on arrival in the area but return to the airport from another location, such as a business they are visiting, or residents who travel to the airport from their workplace but return home from their return flight. Collecting trip egress information requires some thought in questionnaire wording because the egress trip has not yet occurred for residents who are surveyed on the outbound leg of their travel. Air Passenger Surveys 99

5.4.2 Public Transportation Modes Another aspect that requires careful attention is the treatment of public transportation modes in questions about access and egress trips. The use of public transportation is often an important policy issue in situations where airports are trying to reduce or mitigate ground transportation vehicle trips. It can also be a key consideration if one objective of the survey is to support the development of models of airport ground access mode choice. There are two aspects to the use of public transportation modes that may need to be considered in the design of air passenger survey questions. The first is the appropriate definition of the different public transportation services available at the airport. Because different services will have different service areas and may have significantly different levels of service—such as frequen- cies, fares, and hours of service—it will often be necessary to distinguish between the services and not simply classify all such trips into broad categories. Self-completed surveys should avoid the use of terms such as “public transit,” which can mean different things to different respondents. The design of the questionnaire (and the EDCD program where EDCDs are used) should provide the ability to distinguish between different modes and services as necessary. In the case of surveys at groundside access points (discussed in Section 5.9), it may be necessary to develop unique questions or forms for dif- ferent modes. Because of the potential for misreporting the actual public trans- portation service used, it is advisable to specify (or ask for) the name of the agency or firm operating the service and, in the case of local bus services, the number of the route. For other fixed-route services, it may be useful to request the name of the station or stop where the passenger boarded the service. While this level of detail may not be necessary for analyzing the results of the survey, it can be invaluable during data cleaning to correct misreported or misclassified services. In the case of fixed-route services, it may also be helpful to ask how the respondents got to the station or stop where they boarded the service, because this can have a significant impact on the time and cost involved in using the service (e.g., a taxi trip to a transit station could easily cost more than the transit trip itself). While obtaining such information will increase the number of questions to be asked, these generally affect only a small proportion of respondents and so do not have a significant impact on the cost of the survey or the time required to complete it. The second aspect that the survey planning team may wish to explore is the familiarity of the survey respondents with the public transportation system serving the airport. Do air passengers use public transit on a routine basis for other types of trips? This other usage will affect the famil- iarity of air passengers with the local transit system and may affect whether public transit is even considered as an option for getting to the airport. In the case of other forms of public transporta- tion, such as privately operated scheduled airport bus services, air passengers (particularly visi- tors to the area) may not know anything about the services. 5.4.3 Parking Issues Private vehicles are the most widely used means of traveling to or from most airports, and parking revenues compose a major component of airport revenues. Therefore, information on the use of airport parking by air passengers—and those dropping them off or picking them up— is an important aspect of most air passenger surveys. However, survey questions addressing the use of airport or off-airport parking should be carefully worded to prevent misunderstanding by respondents. Careful wording is particularly necessary with self-completed surveys. 100 Guidebook for Conducting Airport User Surveys Although public transportation is often referred to as public transit, at many airports public transportation includes a wide range of services, many operated by the private sector, in addition to the services provided by local transit agencies. Two reports produced under the Transit Cooperative Research Program provide a good overview of the issues involved in public transportation access to airports (Leigh Fisher Associates et al., 2000; Leigh Fisher Associates et al., 2002). Furthermore, transit services may be provided by several different agencies, such as in cases where rail transit service is provided by a different agency from local bus services, or where transit agencies that serve different areas each serve the airport.

The most important distinction to make is between vehicles parked by air passengers for the duration of their air trip and those parked by well-wishers or greeters. This distinction is com- plicated by the frequent practice of airports calling different parking lots or facilities short-term or long-term parking based on pricing and distance to the terminal, rather than the amount of time drivers are allowed to park. Long-term parking facilities may be located some distance from the terminal, and users may think of these as being off-airport, even though they are operated by the airport authority. Then there are privately operated parking lots in the vicinity, which are usually considered off-airport parking. In addition, some airport area hotels may offer parking at competitive rates with the airport. Although most passengers parking a vehicle for the duration of their air trip will use the park- ing facilities designated for daily or longer parking, rather than those for hourly or short-term parking, some passengers making a one-day or overnight trip may choose to use the closest park- ing to the terminal, and pay the higher rate. Finally, some survey respondents may think of a private vehicle standing at the terminal curb for a few minutes while the passengers and their baggage are unloaded as being “parked” for a short while. It is therefore desirable to ask survey respondents to identify the parking facility where the vehicle is parked and the duration that it was (or will be) parked, rather than rely on vague cat- egories such as “parked short term.” These questions should provide response options that use the formal designation of different parking facilities (e.g., hourly parking, economy lot, termi- nal garage), but allow respondents to write in or state other locations if they do not recognize the correct names of the facilities. This will often be necessary anyway in the case of off-airport park- ing, where there may be a large number of different providers. 5.5 Weighting Survey Responses In spite of the survey team’s best efforts to design the sampling plan to obtain a representative sample of air passenger trips, it is very unlikely that the responses will fully reflect the composi- tion of the target population, because of unavoidable consequences of the survey methodology as well as varying response rates by different categories of travelers. Therefore it will be necessary to weight the survey responses in order to improve the accuracy of the resulting data. Because the exact composition of the air passenger population is generally unknown (this is why the survey is being performed), a variety of other types of data is needed to calculate the sur- vey response weights. These data should be assembled at the time the survey is performed—or as soon as possible afterwards—and should include the following: • Enplaned passengers on each flight (if available)20 or enplaned passengers by flight destina- tion for the month in question.21 • Number of connecting passengers on each flight (if available) or estimated from available data.22 • Parking lot exits from each airport parking facility by parking duration and hour for each day of the survey period. Air Passenger Surveys 101 20 Some airports collect these data routinely. Where this is not the case, the airport may be able to obtain this information from the airlines for the period of the survey with an assurance that it will not be made public and only used to help analyze the sur- vey results. 21 These data are available from the U.S. Department of Transportation Bureau of Transportation Statistics T-100 database. 22 Quarterly data on connecting passengers by airline and flight sector can be estimated from the U.S. Department of Trans- portation Bureau of Transportation Statistics Airline Origin and Destination Survey database.

• Automated vehicle information system counts (where available) by class of vehicle (taxis, lim- ousines, shared-ride vans, shuttle buses, etc.) and by hour for each day of the survey period. • Ridership statistics on airport-operated shuttle buses to remote rental car facilities or rail sta- tions by hour for each day of the survey period. Where these are not routinely recorded, it will be necessary to arrange for their collection for the survey period. • Ridership statistics on scheduled airport bus services by run (or hour) for each day of the sur- vey period. Where these are not routinely reported to the airport authority, the airport may be able to obtain them from the operators with an assurance that they will not be made pub- lic and only used to help analyze the survey results. • Terminal roadway traffic counts (where available) by hour for each day of the survey period. Where these data are not routinely collected, consideration should be given to placing traffic counters on the terminal roadways for the duration of the survey. The process of calculating survey response weights consists of two steps: 1. Calculation of weights to correct for known bias in the survey sampling methodology. 2. Calculation of weights to correct for differences between the survey results and external data on traffic composition. Each survey response should include the size of the air party. If the survey responses reflect air passengers (i.e., there are multiple survey responses for parties with more than one passenger), then counts obtained from the survey responses should be divided by the air party size in order to express the traffic composition in terms of air parties. Conversely, if the survey responses reflect air parties (i.e., there is only one survey response for each air travel party), then counts obtained from the survey responses should be multiplied by the air party size in order to express the traffic composition in terms of air passengers. Statistical computer software packages can perform these adjustments very easily in tabulating survey results. The difference between expressing survey results in terms of air passengers or air parties is critically important to the correct interpretation of the survey results and should be clearly understood. 5.5.1 Proportional Weighting Proportional weighting uses weights that adjust the proportions of the survey response data to reflect the proportions of the control data without changing the total number of responses. In general this will result in non-integer counts for many reported survey responses when expressed using weighted data. Proportional weights can only adjust survey response data to correspond to the proportions of a single characteristic of the control data. Separate weights can be deter- mined for different characteristics, but in general it is not possible to determine response weights that adjust survey response data to correspond to the proportions of multiple characteristics of the control data. If there are N total survey responses and ni of those responses reported some characteristic i that composes a proportion pi of the population in the control data, then the proportional weight wi that should be assigned to each of the n responses is given by: Since all N of the survey responses must have reported some value for characteristic i (even if this was only “Don’t know” or “Refused”), a weight wi will be assigned to each survey response. Statistical analysis software can generally be set to optionally exclude missing data cases—such as “Don’t know”—from the tabulated results. However, some users of the results may be interested w p N ni i i = 102 Guidebook for Conducting Airport User Surveys

in knowing the extent of missing data in the survey responses. Therefore, it is better to set the weight for missing data responses to one rather than zero, and adjust the other weights so that the weighted total of the non-missing cases corresponds to the unweighted total of the non-missing cases (i.e., replace N by N minus the number of missing data responses in the above equation). 5.5.2 Correcting for Known Bias in the Sampling Methodology The sampling methodology adopted for the survey may introduce some bias into the response data that can be calculated and corrected. The most obvious example occurs with self-completed surveys handed out to all adult passengers in an airline gate lounge where fewer responses are received from a given air party than the number of passengers in the party. This case will always occur where there are children in the air party (who do not complete the survey). Some passen- ger surveys have asked the respondents to indicate how many members of their air party have completed a survey form and have then used this information to weight the results. However, experience indicates that these statements are often unreliable. Some respondents may misunder- stand the meaning of the term “air party,” while others may not realize that another member of their party is also completing a form. Or they may think that another member of their air party is completing the form, but in fact that form is not turned in. It is therefore preferable (although more time consuming) to examine the survey responses; identify responses from the same party based on the party characteristics, such as their trip origin address or other information; and revise the reported survey completion information before calculating weights to correct for under- reporting of air party members. It is also quite common to apply weights to self-completed survey responses to factor up the responses to the number of passengers boarding the flight. There are two problems with this approach: • It can give a misleading impression of the number of survey responses, as discussed in Sec- tion 5.5.4, unless the resulting weights are normalized to ensure that the total of the weighted responses equals the actual number of survey responses. • It will over-weight responses from under-sampled flights. For example, if generally 50% of passengers on sampled flights are surveyed, but on a particular flight only 10% of passengers are surveyed for some reason, the responses from passengers on the under-sampled flight will be weighted by a factor of 10, rather than the factor of 2 used on other flights. Differences between the distributions of characteristics on a particular flight with only a few respondents compared to other flights in the same market are most likely due to the higher vari- ance that occurs with small samples, not because the characteristics of all the passengers on that flight are different. Scaling up the responses to the total number of passengers on the flight implicitly assumes that all the passengers on the flight have the same distribution of character- istics as the respondents. For example, if only four respondents are surveyed on a particular flight and one of these is leaving on a 10-week trip to Japan, it would be incorrect to infer from this that 25% of the passengers on the flight are leaving on 10-week trips to Japan, but that would be the effect of scaling up the responses. There is of course no way to tell from the results of a survey whether differences in the char- acteristics of the respondents on different flights are due to a true difference or are simply a result of the sampling variance. It is possible to perform statistical tests to determine whether the hypothesis that the results are drawn from the same distribution can be rejected at some level of confidence, but that is not the same thing as knowing that they are different. With a small sam- ple size, the variance in any particular characteristic is likely to be so high that it is unlikely to be possible to reject the hypothesis that the results are from the same distribution as that for other flights in the market at any reasonable level of confidence. Therefore, one is left to make the not Air Passenger Surveys 103

unreasonable assumption that the underlying distributions of the characteristics of passengers in a particular market are the same, and that differences across flights in that market are due to sampling variance. Of course, the distribution of a particular characteristic within each market may vary by other dimensions, such as the time of day or day of the week, further complicating the analysis and reducing the ability to determine whether any apparent differences across flights in the market are simply due to chance. Because passengers on under-sampled flights are likely to be less representative of the character- istics of passengers on other flights in that market, factoring up responses to the total number of pas- sengers on a flight will over-weight those passenger responses that are less representative of the characteristics of the market in question, potentially biasing the results of the survey. Therefore, it is better to consider those passengers who did complete the survey forms as a representative sample of air passengers and make any required adjustment to correct for differences between the survey results and the distribution of air traffic across different markets, as discussed in the next section. In the case of interview surveys, there is likely to be sampling bias that results from the sampling protocol: • A sequential sampling strategy in an airline gate lounge will miss any passengers who arrive in the lounge after surveying has started and sit in areas that have already been sampled. Thus passengers arriving closer to the time boarding begins have a lower chance of being sampled. • If the survey team performs approximately the same number of interviews in each gate lounge, irrespective of the number of passengers on the particular flight, the probability of a given air party being surveyed is lower on flights with more passengers. If the distributions of characteristics of respondents who are over-sampled are the same as those who are under-sampled, the difference in sampling rate will not affect the survey results. How- ever, if the distribution of some characteristic is different, the results will be biased. For example, it is likely that some passenger characteristics, such as trip purpose or air party size, will differ between those arriving in an airline gate lounge well before boarding begins and those arriving shortly before boarding begins. Similarly, if interviews of passengers exiting security screening are performed at approximately the same rate—as is likely with a survey team of a constant size—the result will be a lower sampling rate during busy periods. If passenger characteristics are different between busy periods and slow periods (as is quite likely), the results will be biased. Weights can be calculated to adjust for these sources of bias by examining the results for dif- ferent periods or subgroups of respondents to see if there are any differences in the distribution of characteristics that might vary by period or subgroup. If such differences are found, the sur- vey responses can be weighted by the ratio of the number of air parties or air passengers in each period or subgroup to the number of responses obtained for that period or subgroup. Such weights should be normalized so that the total number of weighted responses is the same as the number of actual responses. 5.5.3 Correcting for Differences Between the Survey Results and External Data Once a set of weights has been determined to correct for known bias in the sampling method- ology, an additional set of weighting factors can be calculated, using the weighted results to cor- rect for differences between the weighted results and external data on the composition of the passenger traffic using the airport. The most obvious potential difference between the survey results and external data on the com- position of the passenger traffic at the airport is if the percentage of passengers in each flight des- tination market given by the survey responses does not agree with the passenger traffic reported 104 Guidebook for Conducting Airport User Surveys

by the airlines. Because connecting passengers may have been sampled at a different rate from originating passengers, it will generally be advisable to consider connecting passengers boarding a flight as a separate market from originating passengers and calculate separate weights for each. Other characteristics of the survey respondents for which it may be worth calculating weight- ing factors include the following: • Airline. • Time of day and day of week of flight. • Ground access mode use by originating passengers. Where several different weighting factors have been calculated for different survey response characteristics, it will generally be advisable to compare the results for each characteristic using the appropriate weighting factor with the corresponding results using each of the other weight- ing factors, in order to determine the sensitivity of the results to the choice of weighting factor. 5.5.4 Weighting for Total Traffic It is common for survey responses to be assigned weights that convert the total number of sur- vey responses to the corresponding count of annual passenger traffic. While this process allows the survey results to be directly expressed in terms of the corresponding annual passenger char- acteristics, two important caveats should be borne in mind before doing this: • The characteristics of the air passenger market at a given airport will vary throughout the year, while the survey data will generally have been obtained at one or two discrete points in time. Thus the resulting data may be quite misleading. For example, if a survey is performed dur- ing August, it will reflect a high proportion of vacation travel. This result is unlikely to corre- spond to the characteristics of the air passenger population during the rest of the year. • Expressing the results of the survey in terms of annual passengers conceals the true size of the survey sample and may give a completely false impression of the accuracy of the results. For example, for a survey with 1,200 responses at an airport handling 12 million annual passen- gers, each survey response is equivalent to 10,000 annual passengers. Thus if the estimated number of annual passengers with some characteristic was given as 22,400 (after weighting for other considerations), it might easily be overlooked that this represents only two survey responses and is likely to be highly inaccurate. Therefore, it is recommended that survey results not be expressed as annual traffic, but rather that weights be calculated so that the resulting totals of weighted responses equal the size of the actual survey sample. It is easy enough for users of the survey results to factor the results up to the level of annual traffic if they so desire, but they will then be fully aware that they have done this and should recognize the accuracy limitations that this implies. One advantage of expressing the survey results in terms of the sample size is that it allows users to easily distinguish whether the results reflect the distribution of air passenger characteristics or air party characteristics, because the response totals will be quite different in each case. For example, if the average number of air passengers per air party is 1.4, a survey with 5,000 air party responses will show results summing to 5,000 when showing the distribution of air party char- acteristics and 7,000 when showing the distribution of air passenger characteristics. If the results are weighted so that the total is equal to the annual passenger traffic, it may be unclear whether they are showing the distribution of passenger characteristics or air party characteristics (which will typically be different).23 Air Passenger Surveys 105 23 If the survey results will be expressed in terms of annual traffic, it is important that results showing air party characteristics be weighted to give the total number of annual air parties, not air passengers.

5.6 Measures to Obtain Adequate Response Clearly, getting people to respond to a survey is an important component of project success. If there are no respondents, there is effectively no survey. In addition, if the response rate is not high enough, it is questionable whether the results should be generalized to the population of interest. Airline passengers are almost by definition in a hurry and stressed. If they are leaving home, they have all the emotions associated with that. If they are returning home, they may be rested and exhilarated from a wonderful vacation or exhausted from a difficult business trip. Regardless, departing passengers have to stand in what are often long lines, deal with security, remember the latest rules or instructions, worry about getting to the gate on time, and actually find the gate. Actually departing passengers are generally inclined to participate in surveys despite the hurry and the stress (at least in part because they usually don’t have anything better to do while stand- ing in line or waiting for their boarding call), but there are still several things the survey plan- ning team can do to maximize the response: • Limit the length of the survey to the number of questions necessary to obtain genuinely needed information. • Make sure that potential respondents understand that the survey is sponsored or sanctioned by the airport, both by the way the interviewers are dressed (perhaps in identifying clothing) and by the content of the introduction. • Emphasize the survey purpose in the introduction, and explain why the information is needed. • Ensure that the questions are clear, comprehensible, and sensitive to concerns about personal information and confidentiality. • Hire interviewers (or people to hand out questionnaires) who are intelligent, personable, and not afraid to approach a wide variety of strangers. • Make sure the interviewers smile as they approach people. • Pay interviewers enough to attract capable people and to ensure they stay for the duration of the project. Aside from the difficulty of replacing interviewers, the longer interviewers stay, the more competent they tend to become. • Provide a thorough and comprehensive training session. • Ensure that interviewers are supervised, monitored, and coached as needed. • Provide retraining as needed. • Utilize positive feedback and incentives to maximize interviewer retention. • Establish and enforce appropriate standards of dress, grooming, and conduct. • Make sure all respondents are sincerely thanked. One other issue that is often raised in this context is the use of incentives for survey respon- dents. Those who have tried respondent incentives are inclined to think they are not worth the cost or the challenge of hauling them around and accounting for them. As noted previously, most air passengers are inclined to participate in airport-sponsored surveys anyway; all airports really need to do to ensure high response rates is make it pleasant for them to do so. 5.7 Location-Specific Guidelines Every airport is different. This section discusses some of these differences and how they can affect air passenger surveys. 5.7.1 Multi-Airport Cities A metropolitan area served by a number of airports presents a problem in determining the characteristics of air passengers with respect to the entire metropolitan area. Analysis at this level 106 Guidebook for Conducting Airport User Surveys

requires a coordinated survey approach at all airports. This coordination does not necessar- ily require simultaneous surveys but does require that the survey method and questionnaire are common at each airport, or the results will not be comparable or applicable to the total population. In general, it would be desirable for the different surveys to be performed within a few weeks of one another to minimize differences due to seasonal effects. A common approach is to conduct surveys at each airport over a period of several weeks, surveying at just one of the airports on any given day and scheduling the days at each airport to provide survey coverage of that airport on each day of the week at some point during the survey period. Stratified sampling could be used to ensure a representative sample across airports and sample sizes chosen so that similar levels of accuracy are obtained for each airport, if comparisons are required. 5.7.2 Multi-Terminal Airports Because different terminals in a multi-terminal airport typically serve different airlines, and often different types of traffic (e.g., domestic or international), a survey that is designed to cap- ture the characteristics of the air passenger population at the airport will need to survey passen- gers in every terminal. In this respect a multi-terminal airport is no different from a multi-airport city. The survey design must account for multiple terminals, with consideration given to an appropriate distribution of the survey responses among the terminals over the course of the sur- vey period. The sampling plan must also consider the multi-terminal environment. Interviewers will require time to switch terminals. Switching terminals may require leaving the secure area and re-entering it, which takes time. These factors must be taken into consideration in designing the survey. 5.7.3 Local Terminology In designing survey questions, it should be recognized that words and phrases may have different meanings, or subtle variations of meaning, in different parts of the country. While it is possible to write a questionnaire using local terminology, many of the passengers will be visitors from outside the region and may misinterpret the questions. It is therefore critical that questions be worded using clear terminology understood by all passengers, and additional explanations given if necessary. With intercept interviews, interviewers must be trained so that they fully understand the questions and, if necessary, can restate a question in local terminology. 5.8 Information on Greeters and Well-Wishers A survey sponsor may wish to gather information on greeters and well-wishers as part of an air passenger survey. Greeters and well-wishers account for a significant proportion of all airport access and egress trips, and some use airport facilities. The distinction needs to be made between greeters and well-wishers who come into the airport terminal building to meet arriving passen- gers or see departing passengers off on their trip, and those who come to the airport only to drop off or pick up passengers but do not come into the terminal. The latter are sometimes referred to as “serve passenger” trips. Although greeters and well-wishers cannot access the secure part of the terminal and thus will not be intercepted by surveys in that area, passengers will be able to provide information on the well-wishers who accompanied them to the airport. However, they may not know how long the well-wishers remained at the airport after the passengers went through security or whether the well-wishers made any use of airport services or concessions before leaving. Air Passenger Surveys 107

Similarly, departing passengers who are visitors to the area may be able to recall information about greeters who met them on their arrival, but they may not know how long those greeters spent at the airport or whether they used any airport services or concessions while waiting. Departing passengers who are residents of the area are less likely to be able to provide informa- tion about greeters who will meet them on their return, because this has yet to take place. Therefore, it may be desirable to survey greeters and well-wishers themselves in non-secure parts of the airport. This is especially true if it would be useful to have information on their use and satis- faction with the facilities, services, and concessions, or to obtain their suggestions. Because it will not always be obvious who are passengers and who are greeters or well-wishers without asking them, information on greeters and well-wishers will generally be obtained as part of a survey that includes passengers as well, but using separate questionnaires or separate questions on a common question- naire. These surveys are typically performed at the various groundside locations. The problems with sampling bias are more acute with greeter and well-wisher surveys than passenger surveys. Well-wishers will often not want to take the time to participate in a survey during the short period they have with the passengers, and they will typically not remain in the terminal long after the passengers proceed though security. Greeters are usually easier to inter- view as they wait for the passenger to arrive, but the sample will be biased towards greeters who spend a longer time at the airport, especially for delayed flights. This bias can result in biased esti- mates of characteristics such as the time spent in the terminal, the time their vehicle is parked, and the amount spent at the concessions. Care must be taken to ensure that greeters and well-wishers are not double-counted when ana- lyzing the results of surveys of air passengers in which multiple responses may be received from a given air travel party. Greeters and well-wishers will usually be at the airport to see off all mem- bers of the air travel party, which must be taken into account when tallying the numbers of greeters and well-wishers per passenger. There will often be more than one greeter or well-wisher meeting or seeing off an air travel party, but only one survey response will be obtained from each group. Thus the number of greeters or well-wishers in the group should be collected, as well as the size of the air travel party they are meeting or seeing off. Care should also be taken in express- ing the results to account for air travel parties that do not have greeters or well-wishers. In the case of well-wishers, this information can be obtained from air passenger surveys. However, esti- mating the number of arriving air parties that are not met is more difficult. The total number of greeters and well-wishers can be estimated by comparing the reported use of short-term park- ing by greeters and well-wishers with statistics on exits from short-term parking by duration. 5.9 Groundside Surveys Groundside surveys form a special type of air passenger survey that can be used to obtain detailed information for planning airport groundside facilities. Groundside surveys are charac- terized by two key factors: first, the survey sample is typically not a controlled random sample of the target population; and second, the interview process is directed at the occupants of a vehicle rather than individual travelers. In the absence of a structured sample plan from which to derive weight factors for each interview, it is necessary to obtain ancillary data in order to calculate appropriate weights for the survey responses. 5.9.1 Purpose Groundside surveys are used to gather information on vehicle use patterns by air passengers and associated greeters and well-wishers to plan future groundside facilities or to create and cal- ibrate a ground transportation model that will be used in future planning studies. 108 Guidebook for Conducting Airport User Surveys

The vehicle trips associated with the passengers on a single flight place loads in time and space on the groundside facilities. The sum of these loads for all flights in a planning period gives the varying load on all groundside facilities, which determines the resulting level of service provided by those facilities. Groundside surveys are designed to collect complete information on the vehicle trips serving arriving and departing air passengers, including the characteristics of the well-wishers and greeters that accompany those passengers. This information enables the development of four time curves associated with air passenger departure and arrival activity: • The time before flight departure that air passengers and any accompanying well-wishers arrive at the airport. • The time well-wishers leave the airport, either before or after the flight departure. • The time that greeters arrive at the airport with respect to the arrival time of the flight they are meeting. • The time that air passengers and any accompanying greeters leave the airport after the flight arrival. 5.9.2 Ancillary Data To handle the sampling rates of this type of survey during the analysis, it is necessary to ensure the survey population is well defined. Groundside interviews will yield air passenger informa- tion linked to specific flights. Therefore, to know how each interview should be factored so that the survey results represent the characteristics of all O/D air passengers, passenger counts should be obtained for each flight. In the case of through flights, it will be necessary to obtain counts of both the terminating and originating passengers. If passenger loads on each flight are not available from the airlines or the airport, they must be estimated using an alternative data source. The airline schedule for the airport can be obtained prior to the survey for the survey period from the OAG or similar sources. This dataset will pro- vide scheduled arrival and departure times, along with aircraft type, from which the number of seats can be estimated. Recent data from the airlines can be used to apply load factors to each flight, by flight sector, to generate estimates of enplaned and deplaned passengers. Since connect- ing passengers do not use the groundside facilities, they must be subtracted to obtain estimates of O/D passengers.24 A key aspect of groundside surveys is that the interview is directed at the occupants of vehi- cles, rather than a group of air passengers. With this in mind, the survey planning team must be able to supplement the interview process with data from traffic counts, possibly in combination with other data sources. The factoring process, involving vehicles as the base unit, requires data from a variety of sources so that the interviews of the occupants of each vehicle can be made rep- resentative of the population. These data sources include the following: • Parking ticket data—to factor the interviews at the parking lots. • Curb activity—to factor the interviews at the curbside, including both the public vehicle area and taxi queues.25 Air Passenger Surveys 109 24 Quarterly data on connecting passengers by airline and flight sector can be estimated from the U.S. Department of Trans- portation Bureau of Transportation Statistics airline Origin/Destination Survey database. 25 Information on conducting curb activity surveys can be found in the documentation for the 2005 Groundside Survey at Toronto Pearson International Airport (see the Bibliography).

• Rental car activity—to factor interviews in the rental car area, both pick-up and drop-off. • Hotel courtesy vehicles, rapid transit, and other public modes—possibly obtained from AVI systems. 5.9.3 Staff Requirements Temporary staff requirements always drive the cost of an interview survey. With groundside surveys there is considerably more latitude in defining these requirements, although the required sample size remains a governing aspect. Whether the survey is covering the entire airport for a short period or covering well-defined segments at different times over a longer period (as discussed in Section 5.9.4), the requirements will be about the same in terms of the total number of interviewer-days. While the calculation of the survey sample size, discussed in Section 5.3, is a key considera- tion, interviewer requirements are also determined by the number of locations that need to be surveyed to ensure representative results. This need for enough interviewers to cover all loca- tions may result in a higher number of survey responses from some locations than is required to meet the minimum requirements for desired statistical confidence. The following interviewer staffing guidelines are based on an extensive groundside survey at Toronto Pearson International Airport in 2005: • Curb area: – Three interviewers per terminal door for a single multi-use curb. – Two interviewers per terminal door for a public use (inner or outer)26 curb area. – One interviewer for each taxi queue (arrivals area). – One interviewer for each of four designated stops for local bus or other services (shared- ride taxi, shuttle services, hotel courtesy, etc.) in arrivals area. • Parking areas: – One interviewer per ticket spitter entrance area for a parking lot, or – Two interviewers per “pay on foot” parking payment machine area. • Rental car and remote parking: – One interviewer per pick-up area, where the rental vehicle is picked up adjacent to the terminal. – One interviewer per drop-off area, where the rental vehicle is dropped off adjacent to the terminal. – One interviewer for each shuttle pick-up area for remote locations where air passengers are picked up adjacent to the terminal by a shuttle service that takes them to a remote or off- airport car rental agency or parking facility. (Where shuttle service for remote or off-air- port vehicle drop-off or parking is provided, the interview coverage is typically provided by the curb interviewers.) • Supervision requirements will vary with the airport configuration and experience of the inter- view staff and should be included in estimating staffing levels. These guidelines should be used in conjunction with the requirements for sample size and the information in Table 5-4 showing the approximate number of responses per interviewer expected under different conditions. 110 Guidebook for Conducting Airport User Surveys 26 Inner curb areas are adjacent to the terminal and, at Toronto Pearson International Airport, are reserved for taxis, limou- sines and the like, while outer curb areas are dedicated to public use.

These estimates are based on the use of well-trained interviewers who can approach a vehicle, engage the party in the interview, and then complete a 20-question interview (including some observation entries) in less than two minutes. 5.9.4 Time and Space Considerations Large international airports have multiple terminals and groundside facilities. Groundside sur- veys must be conducted at numerous locations and across the whole day of airport activity, from 6:00 a.m. (or earlier) to 11:00 p.m. (or later). This time span calls for at least two shifts per day of interviewers. The groundside survey design, however, will not necessarily require that all terminals and all areas be covered at the same time. For medium- to large-sized airports, such a requirement would take an enormous and unwieldy number of interviewers for short periods of time. Instead, the airport or terminal can be subdivided in time and space to make the survey more manageable. For this subdivision process, the survey design must maintain the link to the ancillary data so that the weighting can be completed for the analysis. Air passenger volumes will naturally divide into departing and arriving segments, as well as by terminal, and these volumes can be deter- mined independently. In the analysis, it will then be possible to generate a weighting factor for each interview with a departing passenger as a function of the number of originating passengers. Similarly, the groundside curb areas are often divided into separate arrival and departure areas. Under these conditions it is possible to design a groundside survey that segments the pop- ulation into distinct groups, each of which can be surveyed independently. As an example, consider the following survey plan for a single terminal with an upper level departures area and a lower level arrivals area. The departures level has a single curb, while the arrivals level has an inner and outer curb with taxis and buses at the inner curb and the general public at the outer curb. In addition, there are “pay on foot” parking payment machines at two locations in the terminal, a single lobby for the rental car agencies, no off-site remote service, and a common drop-off location for all rental car agencies. Table 5-4 shows the expected interview Air Passenger Surveys 111 Table 5-4. Number of responses expected per interviewer by groundside location. Area Conditions Estimated Number of Interviews per Eight-Hour Shift Curb—public and taxi drop-off Constant high volume of activity throughout the survey period, first door of the terminal 150 Constant high volume of activity throughout the survey period, second and subsequent doors of the terminal 125 Curb—public and taxi drop-off, public pick-up One peak period of activity and lower volumes during the shift 100 Curb—taxi waiting queue As long as there are passengers waiting in the queue 150 Curb—shuttle stops N/A 80 Parking—ticket spitter Primary entrance to the parking lot; when traffic is heavy, the proportion of vehicles interviewed will be lower 125 Parking—“pay on foot” As long as there are passengers waiting in the queue 150 Rental car—pick-up Single lobby area for multiple agencies, or interviewers move between agencies during shift 100 Rental car—drop-off Common drop-off area for all agencies, or interviewers move between drop-off areas 100 Rental car or remote parking—shuttle service Pick-up area for service to remote area; rate assumes a lower volume of activity than in rental car lobby area 50

completion rates per eight-hour shift for very short, focused interviews conducted by efficient interviewers. Note that completion rates depend on the length of the questionnaire, traffic vol- umes and flows, and the method used to conduct the interviews and, in some cases, may be sig- nificantly less than the rates shown. Actual completion rates will vary over the day, as traffic volumes vary. Table 5-5 shows the corresponding interviewer staffing requirement for this example. Note that fewer interviewers are required for the departures area than the arrivals area, which is quite common. With the interviewer resources established for each area, it is then a matter of making up a schedule of at least two shifts per day, so that the arrivals and departures areas are surveyed an appropriate number of times during the survey period. Based on the required number of inter- views, the number of shifts and therefore the number of days required for the survey can be cal- culated. The shift plan will also have to cover each direction for each day of the week, so that, for example, an early shift for arrivals on each day of the week and an early shift for departures on each day are both included in the survey design, and likewise for the late shift. The survey design should also ensure that staff assigned to a late-night shift are not assigned to the next early-morning shift. It is assumed that week-to-week differences in the traffic pattern will be negligible. With this plan in effect for a terminal with an adequate volume of traffic throughout the day from 6:00 a.m. to 11:00 p.m., each shift of interviewers will perform 1,500 to 2,000 interviews. This example demonstrates why the sample size is less of a concern than the coverage in time and space and the correct weighting of responses. When the survey is conducted over a week or more, the numbers of responses at each individual survey location are usually sufficient for detailed planning purposes. 5.9.5 Questionnaire A generic groundside interview form should be developed first, to lay out the specific ques- tions and establish the overall flow of the form. This form will then be modified to suit each of the interview locations for the survey. Experience has shown that interviewers have difficulties with a generic form that covers both activities that have already occurred and those that are yet to occur. Arriving passengers did some things in the past that departing passengers will do in the future. Keeping the past and future verb tenses in a logical order on a generic form is not easy. Therefore, it is preferable to design forms for each survey location and air passenger direction. The first part of the form will contain observation information that the interviewer can complete as the target vehicle is approached. This information includes the interviewer, interview number, 112 Guidebook for Conducting Airport User Surveys Table 5-5. Example of number of interviewers required. Area Interviewers Departures Area Departures curb—3 doors into terminal 9 Bus and shuttle drop-off 3 Rental car drop-off 1 Arrivals Area Arrivals curb—inner area, 12 stops, plus 2 taxi queues 5 Arrivals curb—outer area, 3 doors 6 Parking payment machines 4 Rental car pick-up lobby 1

time, location, vehicle type, number of occupants, and number of pieces of baggage (where bag- gage is visible). Standard rules for counting people and baggage must be defined, such as: • Any child over the age of two is counted. • All baggage is counted, except purses. After a short introduction, the first question should always be: Have you been interviewed at the airport today? This question has several purposes: to remove undue survey burden on the airport users, to elim- inate duplicate information, and to count the number of vehicles that go to two groundside facil- ities in one airport trip. For departure trips visits to two groundside facilities could involve a stop at the curb followed by entry to the parking lot. For arrival trips it could involve the opposite, with exit from the parking lot followed by a stop at the curb to pick up passengers and baggage. One section of the form will deal with the purpose of the vehicle trip: dropping off air passen- gers, picking up air passengers, or other activities (e.g., buying tickets, using airport concessions, or checking baggage for a later flight). While there will be several response options on the generic form, the number of responses on the form for each survey location may be reduced to a few or only one. For example, at the taxi drop-off or taxi queue areas, there are usually only air passen- gers; therefore, response options that greeters or well-wishers could choose would not appear on the survey form for those locations. Another section will deal with the trip origin or destination within the local area. At departure locations this section typically appears early on the form, whereas with arrival locations this section should be later. These questions will include the type of trip origin or destination and a geographical location, as discussed in Section 5.4. Another section will cover the air trip, which includes the number of air passengers (in this vehicle) as well as the baggage that was (or will be) checked. Experience has shown that air passen- gers usually do not know their flight number, but they do know the airline, where they are coming from or going to, and the approximate time of arrival or departure. A question about whether there will be a transfer en route to the final destination is normally required. This information is usually sufficient to identify the flight on which the air passengers are departing or arriving. A final question will ask whether the air passengers are residents of the area served by the air- port or are visitors to the area. Asking air passengers for their city and zip code (postal code) of residence can allow responses to be classified appropriately without relying on the respondent to decide whether they consider themselves a resident or a visitor, and can provide useful addi- tional information to resolve ambiguous cases. A sample set of groundside interview forms that were used in the 2005 Groundside Survey at Toronto Pearson International Airport is provided in Appendix G. 5.9.6 Calculating Response Weighting Factors Each groundside survey interview will have a number of different response weights attached to it at the time of analysis. These weights will all be calculated from the proportion of interviews to a given population. During the analysis, the appropriate weights can then be applied to the responses. Following is a partial list of weighting factors and the source data that are required to calcu- late the corresponding weights: • Vehicle counts, possibly by mode. Given the total number of private vehicles that stopped at the departures curb and the number of vehicle occupant interviews in a specific time period, Air Passenger Surveys 113

a weight factor can be calculated. The sample percentage will naturally vary with fluctuat- ing demand and a static interviewer resource. Time periods such as one-hour intervals, or peak and off-peak periods, could be used. Thus the weight assigned to each interview dur- ing the morning peak will be higher than the weight assigned to each interview during a slow mid-morning period. A similar approach can be followed for taxis, parking, and other modes. • Passenger counts. Given the total number of originating or terminating passengers, a weight can be calculated based on the number of passengers covered by the interviews compared with this total number. An hourly weight can be calculated using the same approach as that for vehicle counts by time of day. A further refinement on the passenger-based weight factor can be calculated when passenger loads by flight are available, although the caution given in Sec- tion 5.5.2 about the use of flight-specific weights should be noted. Other weighting factors can be specified and calculated, depending on the available data and the goals of the survey. 5.10 Checklists Conducting airport passenger surveys involves numerous people conducting many different tasks. Checklists are a good way of identifying tasks, monitoring progress, and ensuring that all tasks are done. Checklists are particularly useful for organizational tasks involving a number of people. Common types of checklists used in passenger surveys, and examples of items covered, are as follows: • Preparation of contract—defining contract, taking care of legal and administration details, setting survey schedule, preparing the RFP, defining evaluation criteria, determining where to publicize the RFP and/or to whom to send it, holding pre-bid meeting, conducting proposal evaluation and contractor selection (holding interviews if required), informing bidders, nego- tiating contract, obtaining legal approvals and signed contract, holding project initiation meeting. • Questionnaire development—getting input from all parties, preparing initial draft, reviewing, formatting, conducting pre-test and pilot test (including printing or programming EDCDs), making final changes, final printing or programming of EDCDs. • Training—dates, venue (including seating, display boards or projector, etc.), trainers, trainees, other project team members to be present, parking, airport tour (with escort if trainees are not badged), curriculum content, handouts (instructions, questionnaires, procedures, sched- ules, contingency plans, etc.), EDCDs, walkie-talkies, development of interviewing skills, prac- tice interviews, testing, retraining. • Forms and supplies—approvals for conducting survey (as required from airport operator, air- lines, etc.), letter from sponsoring organization authorizing interviewers to conduct survey, printing of questionnaires (different colors for different versions), timesheets for staff, survey log books and flight record log sheets, check-out/check-in sheets for EDCDs, radios and other equipment, pre-paid mail-back envelopes, flight gate schedule sheet. • Logistics—badging of interviewers, organizing of survey field office, equipment for field office (printer, copier, computers, Internet access, telephone, fax machine, power extension cords, etc.), storage space in field office for supplies and interviewers’ personal items, locking and unlocking of field office, vests and/or name tags for interviewers, survey equipment (EDCDs and chargers, pens or pencils, clipboards, and bags), communication equipment (walkie- talkies and chargers), parking for staff. • Contingency plans—interviewers absent or arriving late, cancelled or delayed flights, equipment malfunction (EDCDs, copier, printer, computer, Internet, walkie-talkie, etc.), 114 Guidebook for Conducting Airport User Surveys

bad weather (for groundside surveys outside), abusive passengers, delays at security check- points, uncooperative airline staff, disruptions due to a breach of security or emergency situation. Examples of checklists are provided in Appendix C. 5.11 Survey Budget Given the complexity and variability of air passenger surveys, it would be misleading to offer even a range of budget numbers, let alone an approximate cost per response. Instead, the follow- ing is a list of questions that the survey sponsors will need to answer in order to come up with a realistic budget. 5.11.1 Planning • How many people will be involved in the planning process? • How many of these people will participate at no cost? • How many meetings will there be? • What sort of a meeting space will be required, and can this be obtained at no cost? • Will travel expenses need to be reimbursed? • Will there be beverages, snacks, or meals? • Is parking cost an issue? Will someone need to arrange for parking permits? 5.11.2 Contractor Selection • Who will prepare the RFP? Will this time be charged to the project? • Who will evaluate proposals? Will this incur any costs? • Will there be a pre-bid meeting? Will this incur any costs? • Will bidders be interviewed? Who will be on the interview panel? Will this incur any travel expenses or other costs? • Will the staff time involved in contract negotiation and approval be charged to the project? 5.11.3 Questionnaire Design and Testing • Who will be responsible for questionnaire design? • How long will the questionnaire be? • Will the questions be easy or difficult to craft? Is a previous or similar questionnaire available? • Will the survey be programmed into EDCDs? If so, who will do the programming? Will this incur any costs? • How many people will test the programming of the EDCDs, if used? Who will do this? Will this incur any costs? • How many completed interviews will be collected during the pre-test? • Where will the pre-test staff be briefed and debriefed? • Where will the pre-test be conducted? • Who will be involved in the pre-test and at what hourly rates? • If there is no programming, how many copies of the draft questionnaire will be required? • Will mileage, per diems, or other travel expenses be required for pre-test staff? • Will parking cost be an issue? Will someone need to arrange for parking permits? • Will there be a supplemental hand-out/mail-back questionnaire? What printing costs will be involved? What postage costs will be incurred? Air Passenger Surveys 115

5.11.4 Sampling Plans • Who will prepare the sampling plan for each day? How long will this take? (It will take longer than you think unless you have done it before.) • How will the sampling plan be transmitted to the survey field team? • Who will make sample adjustments as contingencies arise? How will these adjustments be communicated to the parties who need to be aware of them? • How will the project adjust if sample quotas are not met, and who will be responsible for doing this? • How many adjustments are likely to be made, and what are the implications for additional survey days? 5.11.5 Badging • How many field staff will need to be badged? • Who will be trained in the badging requirements and make the badging arrangements? • How long will each field staff member need to spend on the badging process? • What contingency plans will be needed for field staff who do not pass the background check? • Is parking cost an issue? Will someone need to arrange for parking permits? 5.11.6 Training • Will field staff need to be trained? • How many interviewers will need to be trained? • How many other staff will be involved, and who will they be? • How many days or hours will the training take? Will it take place over more than one day? • What training materials will need to be reproduced? • What sort of training space will be required, and can this be obtained at no cost? • Will mileage, per diems, or other travel expenses be involved? • Will there be beverages, snacks, or meals? • Is parking cost an issue? Will someone need to arrange for parking permits? 5.11.7 Pilot Testing • What aspects of the survey will be pilot-tested? • Who will conduct the test? • Who will conduct the debriefing and make adjustments as needed? • Where will the debriefing take place, and can this space be obtained at no cost? • What is the contingency plan if the pilot test reveals problems that need to be addressed? Will this have any impact on costs? 5.11.8 Survey Implementation • How many interviews will be completed or forms handed out and returned? • On how many days will the survey take place? • How many hours per day will need to be covered? Will very early and very late flights be included? If they are included, who will cover them? • What shifts will be involved on each day? • How many interviewers will this require? • How many supervisors will be required based on shifts, airport configuration, and walking distances? What will the supervisors’ responsibilities be? 116 Guidebook for Conducting Airport User Surveys

• What are the pay rates for interviewers and supervisors? Will pay rates be higher for very early morning and late-night hours? • Where will the field staff be based at the airport? Will this location provide for ready access, charging of electronic devices, security, and storage of both supplies and personal effects for those in the field? Will this incur any costs? • Will field staff wear uniforms or identifiable clothing (e.g., vests or aprons)? • What supplies will be required? • Will it be necessary to purchase or rent EDCDs and chargers, or other electronic equipment? Do the EDCDs come with adequate software, or will software need to be purchased? • How many copies of questionnaire forms will be required? • Will show cards be used? How many sets will be required? • Is there a supplemental hand-out/mail-back questionnaire? What printing costs will be involved? What postage costs will be incurred? 5.11.9 Quality Control • Who will be responsible for checking completed work? • What percentage of all work will be checked at the beginning? As the project progresses? When will this take place? (Beware of overtime!) • What logic checks will be performed? Who will develop the protocols for these checks? • How will completed and checked work be transmitted to the survey sponsor or technical expert for further review? At what frequency will this occur? • How much time will these further checks take? (Again, likely more than you think unless you have done this before, particularly for a survey involving geocoding trip origins.) 5.11.10 Data Entry and Verification • Will completed questionnaires need data entry? • How will data entry be accomplished? • How many mailed-back forms are likely to need processing? • Will the data entry be verified? In what way and in what amount? 5.11.11 Analysis and Reporting • What sort of report will be required? • Who will prepare statistical tabulations or any computations needed? • Will statistical software need to be purchased? • Who will prepare the graphics? How many graphics will there be? • Who will write each section of the report? • How many sections will there be, and how long will each one be? • Will there be an oral presentation? • Will this presentation incur costs such as mileage or airfare, car rental, parking, and per diems? 5.12 Summary Air passenger surveys are the most common type of airport user survey, but they involve many complex issues that need careful consideration if the results are to be useful and accurate. These issues include the following: • Whether to interview passengers or use self-completed survey forms. • Where to perform the survey. Air Passenger Surveys 117

• When to perform the survey and over how long a period. • How large a sample size to aim for. • Development of an appropriate sampling plan. • Development of a well-designed and carefully worded questionnaire. • Selection and training of field staff. • Planning of survey logistics. • How to weight the survey responses. Because air passenger characteristics vary by hour of the day and day of the week, passenger surveys should generally take place over at least a full week and cover all hours of each day. These surveys are best conducted either in the airline gate lounges before a flight departs or as passen- gers arrive or depart from the security screening area. The choice of location will depend on fac- tors such as the survey population, the types of information being collected, the layout of the terminal(s), and the survey method used. The fact that many passengers will be traveling as part of a group needs to be considered in designing an air passenger survey. Self-completed surveys are usually handed out to every passen- ger on a selected flight (or at least those waiting in the gate lounge), while interview surveys gen- erally interview only one person from each air travel party. This difference needs to be reflected in the questionnaire design, sampling plan, and analysis and reporting of the survey results. Even with the most carefully designed sampling plan, it is inevitable that the resulting survey responses will not exactly correspond to the composition of the underlying target population. Some passengers will be over-sampled and some will be under-sampled. In particular, it is likely that those passengers arriving at the gate close to flight departure time will be under-sampled. Over-sampling or under-sampling may also result from variations in aircraft size, flight load fac- tors, or constraints of the sampling plan. Therefore, it will generally be desirable to weight the survey results. Calculation of appropriate weights requires careful thought and the collection of ancillary information about the target population that can be used to determine the extent of any bias in the survey responses. Groundside surveys of vehicle occupants form a special type of air passenger survey that can be used to obtain detailed information for planning airport groundside facilities. These surveys— which provide information on greeters and well-wishers as well as passengers—are performed at various locations on the airport landside, including terminal curbs, parking facilities, and shuttle bus or public transportation pick-up and drop-off stops. Because the sampling rate varies widely from location to location and time to time, the results need to be weighted using counts of vehi- cles at different facilities as well as counts of originating and terminating air passengers. Finally, this chapter has discussed the logistical issues involved in conducting air passenger surveys and estimating the cost of planning and performing such a survey. 118 Guidebook for Conducting Airport User Surveys

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TRB’s Airport Cooperative Research Program (ACRP) Report 26: Guidebook for Conducting Airport User Surveys explores the basic concepts of survey sampling and the steps involved in planning and implementing a survey. The guidebook also examines the different types of airport user surveys, and includes guidance on how to design a survey and analyze its results.

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