Estimating the Value of Truck Travel Time Reliability (2019) / Chapter Skim
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4 This chapter reviews the literature to build an understanding of how roadway unreliability affects shippers and motor carriers, focusing on previous attempts to estimate the VOR. The chapter focuses on freight, but several studies on the reliability of passenger transportation are also reviewed.
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Background 5 Unreliability in travel time can be caused by demand factors that affect vehicle volumes or supply factors that affect system throughput (Mahmassani et al.
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6 Estimating the Value of Truck Travel Time Reliability travel time over 50th percentile travel time) , the buffer index (95th percentile travel time over average travel time)
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Background 7 showed how unreliability can affect firms in many ways, leading them to adopt various short- and long-term strategies to cope with the uncertainty. A delayed shipment can generate the following costs: • Transportation costs: These costs, which result from trucks taking longer to make a delivery, include driver wages, fuel, maintenance, and so forth.
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8 Estimating the Value of Truck Travel Time Reliability which no cost was accrued, a point at which delay costs increased rapidly, and a point at which contingencies had been activated and further delays were not costly. Early arrivals can also be problematic if, for example, there is not enough space to accommodate incoming trucks.
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Background 9 positive events in defining preferences. Carrel et al.
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10 Estimating the Value of Truck Travel Time Reliability • Firm sophistication. Sophisticated firms are likely to respond more effectively to unreliability because they likely have better technology, greater familiarity with routes (and knowledge of traffic conditions)
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Background 11 VOT and VOR is challenging because travel time and reliability are goods that are not traded in markets and therefore are not priced by the supply–demand equilibrium. There are essentially two ways that nonmarket goods such as these can be valued: They can either be (1)
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12 Estimating the Value of Truck Travel Time Reliability 2.2.2 Stated-Preference Studies Interest in estimating the VOR of trucking has picked up in the past couple of decades. Reliability had always been known to be important for freight, but only as surveying capabilities improved and models became more flexible has estimating VOR become possible.
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Year Author(s) Place Reliability Measure Modes Heterogeneity Survey Sample Size 1981 Winston United States Travel time coefficient variation Road and rail Commodities and modes RP data ~2,500 shipments 1999 Small et al.
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14 Estimating the Value of Truck Travel Time Reliability adaptive surveys have undesirable statistical properties that make it difficult to estimate the VOR (discussed further in Appendix A, Section A.2)
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Background 15 2.2.2.3 Limitations Stated-preference surveys can be affected by several well-known biases (see Ortúzar and Willumsen 2001 for a review)
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