Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
90 Survey Responses A P P E N D I X B Appendix B describes in greater detail the results of the stated-preference survey. The survey was completed by 1,142 respondents who provided answers to 18,096 hypothetical stated- preference questions. Figure B-1 shows that some respondents provided unrealistic responses in terms of shipment costs or average speeds. To improve the quality of the data, a minimal number of cleaning actions was undertaken (see Section 3.4), which reduced the sample to 982 responses. Most responses came from self-identified motor carriers, which represented 59 percent of the sample (Figure B-2). Shippers without transportation represented 11 percent of the sample and shippers with transportation represented the remaining 30 percent. Obtaining a signifi- cant number of responses from each of these types was a key accomplishment of the survey. As can be seen in Figure B-3, most respondents belonged to companies with just one to four employees, although a significant sample was also achieved for larger companies. Most of the smaller companies were classified as motor carriers, which likely represents owner-operated trucks (Figure B-4). Figure B-1. Scatter plots showing outliers in recent typical shipment costs, length, size (tonnage), and average speed.
Survey Responses 91 Figure B-2. Respondents by type. Figure B-3. Respondents by company size (number of employees). 0 50 100 150 200 250 300 350 400 450 1-4 5-24 25-100 100-1000 1000+ N um be r of R es po nd en ts Company Size (# employees) Motor Carrier Shipper w/o Transportation Shipper w Transportation Figure B-4. Respondents by company size and type. Table B-1 describes how shipment characteristics varied across the three respondent types. Shippers without transportation reported significantly longer distances and hours of travel, while motor carriers reported larger shipments. Figure B-5 shows the commodities reported as being transported in the recent typical ship- ment. As can be seen in this figure, these commodities span a wide range of industries and eco- nomic sectors, thereby giving the survey a robust representation of freight activity nationwide. A substantial sample was achieved in sectors typically associated with high values of reliability, such as miscellaneous manufactured products, machinery, meat/seafood, agricultural products, and electronics. On the right of this figure can be seen the distribution of tonnages moved by truck in the United States in 2015, as reported by the Freight Analysis Framework (v. 4.4). The survey captured shipments of all lengths. As can be seen in Figure B-6, about half of the shipments were shorter than 500 miles, and the other half spanned a wide range of lengths,
92 Estimating the Value of Truck Travel Time Reliability including several transcontinental shipments over 2,500 miles. Over 250 respondents described a reference shipment less than 100 miles, which most likely corresponds to urban deliveries or drayage. Shipment distance was also used in the modeling to reweight the sample to achieve more representative results. The survey also asked about the destination of these shipments, as this can have a large effect on reliability valuations. Figure B-7 shows that the majority of respondents described shipments going to customers. Around 200 reported shipments to themselves, and the remainder to a variety of intermodal terminals (sea, air, rail), and other. The size and cost of the reference shipments can be seen in Figure B-8. Respondents were instructed to only include the truck portion if multiple modes were used. Most shipments cost less than $2,000, although higher responses were recorded. Almost 50 percent of shipments cost less than $500. There was a strong correlation between cost and size. The survey captured a combination of less-than-truckload shipments and truckload shipments over 16 tons. Some respondents described very large shipment sizes, of almost 40 tons, which corresponds to either oversized loads or respondents mistakenly including the gross weight of the trucks. Having the appropriate individuals take the survey is a key challenge when surveying compa- nies, and even more so when eliciting stated-preference responses that attempt to mimic actual decision-making. In the present study, individuals were sought who either were involved in making shipping decisions on a day-to-day basis or who operated trucks. To determine whether the right people were reached, respondents were asked to describe their title and responsibili- ties (Figure B-9). Most respondents identified themselves as owners, which in most cases refers to truck ownerâoperators. There were also logistics managers, fleet operations managers, and coordinators among those surveyed. Overall, 94 percent of respondents indicated that they were involved in making transportation decisions at their companies, which suggests that the survey was taken by the appropriate people. Shipment Characteristic and Type of Respondent N Mean SD Median Skew Min. Max. Distance (mi) Motor carrier 576 676 678 450 1.52 10 3,200 Shipper w/o transportation 109 875 761 700 1.22 18 3,200 Shipper w/ transportation 297 351 493 150 2.52 5 3,000 Time (h) Motor carrier 576 18.5 28.3 10.5 9.56 0.3 504 Shipper w/o transportation 109 33.1 32.7 22.0 1.07 1 125 Shipper w/ transportation 297 10.6 15.4 5.0 3.09 0.25 102 Weight (tons) Motor carrier 576 17.1 9.9 20.0 0.05 1.0 50.0 Shipper w/o transportation 109 9.9 9.5 5.5 0.52 0.1 39.0 Shipper w/ transportation 297 12.1 12.0 8.0 0.96 13.0 50.0 Cost ($) Motor carrier 576 1,195 1,420 750 3.56 0.01 15,000 Shipper w/o transportation 109 1,535 1,433 1,200 1.22 20 6,500 Shipper w/ transportation 297 794 1,095 380 2.51 10 6,600 Table B-1. Descriptive statistics for shipment characteristics.
Survey Responses U.S. Truck Shipments Figure B-5. Commodity distribution of recent typical shipments and U.S. truck tonnages (Freight Analysis Framework, v. 4.4). Figure B-6. Length of reference shipments.
94 Estimating the Value of Truck Travel Time Reliability Figure B-7. Destination of reference shipments. (a) (b) Figure B-8. Reference shipment (a) cost and (b) weight. Are you involved in making transportation decisions? Figure B-9. Title and function of respondents. At the end of the survey, respondents were asked to rank the relevance of the hypothetical choice questions in their daily operations. As can be seen in Figure B-10, 682 of the respondents indicated a relevance of at least 3 on a 5-point scale, which suggests that the majority found the stated-preference questions relevant. As can be seen in Table 3â4, six of the 25 choice questions were trivial, in that one alterna- tive was clearly better than the other one. These questions were not removed, so as to preserve
Survey Responses 95 the favorable statistical properties of the survey and to test whether respondents made logi- cal selections. Ultimately, 83 percent of the trivial questions were answered correctly, which is typical of surveys of this type. Out of all the responses, 70 always selected the cheapest alternative, 35 always selected the fastest alternative, and 34 always selected the most reliable alternative. This indicates that most respondents made trade-offs between the hypothetical attributes presented. Figure B-10. Responses by relevance of stated- preference questions. Note: From 1 (lowest) to 5 (highest), rate the relevance of the eight sets of hypothetical alternatives provided. Were the choices presented realistic and representative of what you face in making shipping decisions?
Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACIâNA Airports Council InternationalâNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing Americaâs Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation
TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-48088-8 9 7 8 0 3 0 9 4 8 0 8 8 8 9 0 0 0 0 N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 Estim ating the Value of Truck Travel Tim e Reliability N CH RP Research Report 925 TRB