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58 der data." However, the primary disadvantage of GPS Semifrequent callers--trucks that visited at least is the relatively small number of GPS-equipped trucks every other day (30.3%) and, accordingly, "in a large metropolitan region insuf- Nonfrequent callers--trucks that visited less than ficient data may be collected on many routes unless a once every other day (19.3%) (53). fairly large sample of trucks actively participates in the data collection effort." Also, the GPS data collection requires "considerable staff effort" to coordinate, and COMPARISON OF TECHNIQUES a "mechanism for recruiting trucking company partici- pation" is required (50). The second paper noted that Some of the case studies described earlier compare alter- CVISN-AVI-equipped vehicles were much more com- nate survey techniques, whereas others combine several mon and little labor was required to retrieve the data techniques. A definitive description of the circumstances (compared with GPS), but data could be collected only under which a particular type of survey should be used does at routes equipped with CVISN-AVI readers at weigh not exist. However, three recent comparisons provide some stations. Moreover, the data cover several trucks across guidance. They also illustrate the complexity of the topic long stretches of road, and specific points of congestion and demonstrate how the definition varies according to the can be difficult to locate (51). perspective. A 2007 research survey in Peel Region, Canada (a sub- urb of Toronto), included a tour information form that A 2001 study identified two survey types among three was to be completed by the responding establishment's types of truck data collection methods: roadside intercept drivers. The form began with information at the start surveys and travel diary surveys. The third method is vehicle location; that is, the work location where the driver's classification counts. The three methods and the associated "work day" began. Some of the vehicles were fitted with characteristics are listed in Table 28 (54). The roadside inter- GPS units to enable comparison with the paper driver cept and the travel diary surveys have long been used as an surveys. The combined data also were used to describe analytical basis for truck trip generation rates and model- tours. The paper surveys faced significant stop non- ing, and they often are accompanied by vehicle classification reporting issues, such as truncated surveys, stops that counts (in part to expand survey samples). This categoriza- were missing in the middle of a tour, and incorrectly or tion also has been cited and expanded by other sources [e.g., inaccurately recorded stop location information. At the (9)], but the general basis is common. However, the perspec- same time, the GPS units provided a useful level of pre- tive is that of quantitative analysis and modeling which, cision but did not capture well stops of short duration although important, represents only part of the picture. (of less than 5 minutes, which comprised a significant portion of the stops). Also, small differences in the A 2004 study in Portland, Oregon, compared differ- identified (compared) stop locations resulted in some ent truck trip data collection methods (9). One test exam- misinterpretations of the actual tour (52). ined roadside surveys along a highway, at a marine port, Finally, a 2006 study proposed the use of optical char- and at a private transportation depot/distribution center. acter recognition (OCR) technology to collect vehicle Another series of tests examined different combinations license plates from trucks accessing selected terminals of self-completion surveys (i.e., different combinations of at the ports of Los Angeles and Long Beach. The pur- mail-back or facsimile surveys with telephone contact and pose of the data collection was to develop an initial follow-up), with surveys sent to "known" samples (that is, estimate of heavy-heavy-duty diesel truck activity and establishments with which the sponsoring authorities had population, for application to the San Pedro bay Ports an established working relationship regarding other freight Clean Air Action Plan. To develop the estimate, data initiatives) and "unknown" samples (freight establishments were collected for a continuous 37-day sample at five without a prior contact). container terminals. The sample was considered rep- resentative of the Ports' 14 terminals. The OCR data The roadside surveys experienced high response and com- were first analyzed to identify unique license plates pletion rates at all three locations, with some qualifications: and then to obtain the frequency of access to the Ports. the preponderance of container traffic at the port limited the The analysis yielded 15,700 unique license plates that driver's knowledge of payload information, obtaining detailed comprised more than 253,000 trips. Of these, only origin-destination addresses was difficult for all interviews vehicles registered in California were retained, result- (though less so for the distribution center interviewees), and ing in approximately 12,000 vehicles and 244,000 trips finding large numbers of private firms to participate in this that were used in the analysis. The remaining truck and type of survey could prove challenging (9). trip records were categorized into three groups: Frequent callers--trucks that visited the terminals The mail-back and facsimile surveys presented more one or more times daily (50.4%) challenges, although they provided valuable information. There was no measurable difference in the response rate

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59 or in the quality of the information between the known and not of completed questionnaires (in other words, increased unknown samples (i.e., familiarity did not make a differ- contact was associated with increased refusal rates). Nonre- ence). Both contained a "very high" percentage of incor- spondents comprised almost half the known and unknown rect and invalid information. The pre-survey and follow-up samples; follow-up contact might improve response rates. telephone contacts improved response rates overall, though Respondents provided several reasons for not participating, TABLE 29 METHODS BY WHICH URBAN FREIGHT SURVEY TECHNIQUES CAN BE CONDUCTED 1. Establishment surveys (surveys of the Self-completion (post, fax, or e-mail) shipments made by businesses--the shippers Self-completion (post, fax, or e-mail with initial and reminder phone call) and/or receivers of goods and services, with specific origin-destination information) Self-completion (left and collected in person) Telephone interview Face-to-face interview 2. Commodity flow survey (surveys of businesses Self-completion (post, fax, or e-mail) on the quantities of goods shipped. Can include Self-completion (post, fax, or e-mail with initial and reminder phone call) some origin-destination information) Self-completion (left and collected in person) Telephone interview Face-to-face interview 3. Freight operator survey (surveys of logistics Self-completion (post, fax, or e-mail) managers of businesses or of carriers regarding Self-completion (post, fax, or e-mail with initial and reminder phone call) the fleet's activities, including origin- destination) Self-completion (left and collected in person) Telephone interview Face-to-face interview 4. Driver survey (surveys of a driver's activities Self-completion (left in person) on his/her rounds for a given period) Face-to-face interview 5. Roadside interview survey (surveys of the Face-to-face interview vehicle's activities for the trip being made when the vehicle is stopped for the interview) 6. Vehicle observation survey [observations by In-person observation others of a vehicle's activities at a given site(s). Observation using film/camera Does not necessarily involve the vehicle driver] 7. Parking survey (observations by others of a In-person observation vehicle's activities while it is parked or being Observation using film/camera loaded or unloaded at a stop) 8. Vehicle trip diaries (surveys of a vehicle's Self-completion (post, fax, or e-mail) activities on its rounds for a given period. Self-completion (post, fax, or e-mail with initial and reminder phone call) Similar to the driver survey but specific to the vehicle) Self-completion (left and collected in person) 9. GPS survey (electronic surveys of a vehicle's Equipment/transmitter fitted in vehicle exact location. Also captures travel times) 10. Suppliers survey (surveys of supplier Self-completion (post, fax, or e-mail) businesses--suppliers to the supply chain--on Self-completion (post, fax, or e-mail with initial and reminder phone call) the goods being shipped and on the supporting vehicle activity) Self-completion (left and collected in person) Telephone interview Face-to-face interview 11. Service providers survey (surveys of services- Self-completion (post, fax, or e-mail) generating businesses regarding the Self-completion (post, fax, or e-mail with initial and reminder phone call) characteristics of its employees' trips. Similar to freight operator survey but specific to Self-completion (left and collected in person) services) Telephone interview Face-to-face interview 12. Vehicle traffic counts Manual (in-person) counts Automated counts (using sensors, film, cameras, or other technology) Source: Allen and Browne (2008) (2).

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60 TABLE 30 ADVANTAGES AND DISADVANTAGES OF METHODS FOR CONDUCTING URBAN FREIGHT SURVEYS Survey Method Advantages Disadvantages Face-to-face interviews and telephone surveys High response rate compared with self- More expensive and time consuming per (for wide range of survey techniques including completion due to personal contact respondent than self-completion (especially establishment, commodity flow, vehicle operator, Can provide better quality, more detailed face-to-face interviews) shipper, and service provider surveys) information than self-completion method Can prove too expensive for a large sample Provides opportunity to query responses size (especially face-to-face interviews) Good for open-ended questions and Often difficult to obtain initial and in-depth discussion about responses participation and requires call backs Easier to make follow-up contacts Telephone surveys offer better opportunity to survey over large geographical area than face-to-face interviews Face-to-face interview allows more in-depth discussion and use of other techniques (such as supply chain mapping etc.) Self-completion surveys Lower cost method than interviews of Generally lower response rates than with (for wide range of survey techniques including self-completion with initial contact interviews or self-completion with initial establishment, commodity flow, vehicle operator, Permits larger and more representative contact. shipper, and service provider surveys) samples than interviews Difficult to ensure that right person in Offers better opportunity to survey over organization will respond large geographical area than face-to-face No way of knowing whether respondent interviews understood question in way intended No opportunity to check/clarify or discuss responses Difficult to interpret nonresponses to questions Not good for open-ended questions Self-completion with initial contact and Lower cost method than interviews-- More expensive than basic self completion reminder by phone call or in person effective method method (for wide range of survey techniques including Can provide better response rate than Other disadvantages same as basic self- establishment, commodity flow, vehicle operator, basic self completion method completion method shipper, and service provider surveys) Phone/in-person follow-up can allow opportunity to clarify/discuss responses (but difficult to achieve in practice) Offers better opportunity to survey over large geographical area than face-to-face interviews Roadside (face-to-face) interviews instead of High response rate Disruption to traffic flow vehicle trip diaries (self-completion) Can provide information on trip purpose, Staffing requirements are high, making it (for obtaining vehicle journey data) goods carried and origin/destination, and expensive route No opportunity for follow-up with respondents Requires involvement of police and/or other bodies Does not provide details about entire journey and stops In-person observation instead of using film/ Reduced potential to cause traffic/ Staffing requirements are high, making it camera delivery disruption expensive (for vehicle observation/parking surveys) No risk of equipment/ recording failure Limited to hours/days of observation, so does Provides actual data about number and not capture all activity timing of deliveries and collections, Neither in-person nor film observation can unlike establishment survey capture all delivery and collection activity, especially not of vehicles stopping off-street or in side roads Manual traffic counts instead of automated Reduced potential to cause traffic Staffing requirements are high making it traffic counts disruption expensive Complete disaggregation of vehicle type Difficult to collect traffic count data at many possible if trained surveyors used locations without it being very expensive Vehicles not wrongly identified No risk of equipment failure Source: Allen and Browne (2008) (2).

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61 including privacy, inapplicability, lack of time, or unavail- Manual traffic counts instead of automated traffic ability of an appropriate person at that location. Information counts (i.e., to distinguish vehicle types in the counted related to trip detail for inbound and outbound shipments traffic). This technique is identified in the source docu- was the most difficult to obtain through the mail survey (9). ment as being relevant to urban freight surveys; how- ever, it is not a survey type in itself. Given these findings, and noting that these were pilot tests that were based on small samples, the study made sev- Table 30 compares the survey types' relative advantages eral recommendations (9): and disadvantages (2): Establish an updated freight contact list to improve the Face-to-face interviews enable a high response rate, response rates and quality. can provide better quality information and details, Use roadside interviews as the basis for data collection enable open-ended discussion and probing, and allow for "inter- and intra-regional freight movements" at the for both quantitative and qualitative input. However, three types of locations (highway, terminals, and pri- they are expensive and time consuming. vate warehouse/distribution centers), and ensure that Telephone surveys have the same advantages as face- the survey sites are geographically distributed in the to-face interviews, and though they are also time con- metropolitan (Portland) area. suming they can provide a less expensive means of Use the mail-back/facsimile surveys of warehouses/ capturing a larger sample size (per unit cost). distribution centers to complement the roadside inter- Self-completion surveys have low unit costs and views and gather selected pieces of information (nota- can reach a larger number of respondents. However, bly, about the activity at the facility's location, and not response rates typically are lower, and there is no con- about the trip detail). trol over the actual response, its level of detail, accu- Use improved survey design techniques to improve the racy, or quality (i.e., questions can be misinterpreted response rate. or omitted), or whether the appropriate person is Employ all possible follow-up techniques, subject to responding. budget. Self-completion surveys with telephone or in-person follow-up provide the opportunity to improve response Finally, a 2008 review of urban freight surveys compared rate, clarify the questions, and otherwise guide respon- survey techniques. Table 29 lists the techniques that are dents in completing the survey properly and com- most commonly used for 11 survey types (and also includes pletely. However, this approach is more expensive than vehicle traffic counts, because these commonly complement the stand-alone self-completion surveys. survey activities). The following are six basic survey tech- Roadside interviews have a high response rate and niques (2): allow for solicitation of detailed information of the trip at hand. However, they disrupt traffic flow, are expen- Face-to-face interviews (i.e., at the establishment loca- sive (because of staffing requirements), and are able to tion) and telephone surveys. gather only limited information beyond the immediate Self-completion surveys (mail-back or on the trip. Internet). In-person observations (compared with filming or Self-completion survey, with initial contact and fol- camera) provide data on actual conditions. However, low-up reminder by telephone or in person. they are expensive and are limited to the actual times Roadside (face-to-face) interviews, as distinct from of observation (i.e., no supplementary data). self-completed driver surveys or vehicle trip diaries. Manual traffic counts (compared with automated traf- In-person observation, instead of using film or camera fic counts) provide accurate data on vehicle types. (for vehicle observation or parking surveys; also has However, staffing requirements make them expensive. been used to capture driver or vehicle activity, through people accompanying the driver on his/her rounds).