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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

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Air Passenger Surveys 75 Table 5-1. Information obtained in a sample of air passenger surveys. DIA MWCOG LAWA MTC Question 1999 2000 2001 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 WashingtonBaltimore 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. 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).

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76 Guidebook for Conducting Airport User Surveys 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. 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

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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.

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78 Guidebook for Conducting Airport User Surveys (a) Oakland International Airport Resident Business Resident Personal Visitor Business Visitor Personal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Mon Tue Wed Thur Fri Sat Sun Day of Week (b) San Francisco International Airport Resident Business Resident Personal Visitor Business Visitor Personal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Mon Tue Wed Thur Fri Sat Sun Day of Week 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.

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(a) Oakland International Airport Resident Business Resident Personal Visitor Business Visitor Personal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24+ Hour (b) San Francisco International Airport Resident Business Resident Personal Visitor Business Visitor Personal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24+ Hour 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.

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80 Guidebook for Conducting Airport User Surveys 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.

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Air Passenger Surveys 81 3 2 Podium 1 1 4 Interviewer 1 3 Interviewer 2 2 7 6 Podium 1 2 3 4 5 Interviewer 1 Interviewer 2 5 4 3 2 1 Figure 5-4. Typical respondent sampling sequences in airline gate lounges. 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.

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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.

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Air Passenger Surveys 83 Table 5-2. Representative follow-up questions. 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.) 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

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84 Guidebook for Conducting Airport User Surveys 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.

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Air Passenger Surveys 85 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.

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86 Guidebook for Conducting Airport User Surveys 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-

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Air Passenger Surveys 87 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

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88 Guidebook for Conducting Airport User Surveys 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

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Air Passenger Surveys 89 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