Distribution of the Value of Travel Time Savings
The value of travel time savings (VTTS) is a critical input to benefit-cost analysis, understanding traveler behavior, and determining the best use of transportation capital funds. How to select a proper VTTS has been the subject of numerous empirical and modeling studies, however almost all such investigations have produced average values for the entire urban population or for large subgroups of travelers. There also exists some research on the value of travel time reliability, which is a closely related although distinct consideration.
The use of average VTTS has the virtue of being simple and avoiding certain pitfalls related to social equity, in which planning recommendations might otherwise be dominated by benefits gained by extremely high value-of-time travelers, who may disproportionally include the rich. The problem with the average VTTS approach is that it assumes a normal distribution when the actual distribution may be skewed.
Improved knowledge of disaggregate VTTS variations within a given traveling population is of increasing interest with regard to understanding travel behavior, especially due to a growing national interest in incorporating innovative pricing elements within transportation planning alternatives. If the actual VTTS distribution is indeed skewed, which is likely given that the income distribution is negatively skewed, the traffic redistribution and revenue consequences of pricing measures will be incorrectly estimated.
Evidence suggests that an individual’s value of time saved, while related to income and other demographic characteristics, varies considerably for the same individual on different occasions. This can be seen in patterns of use of optional express toll facilities (e.g., HOT lanes) where the same people make different route choices on different days, even where amounts of travel time saved by selecting the congestion-free toll facility are essentially the same. Clearly, in addition to demographics, the VTTS of individuals depends on factors such as trip purpose, the magnitude of time saved per trip, who pays (traveler, the traveler’s employer, etc.), and the possibility of engaging in other productive or pleasurable activities while traveling.
Several areas that merit additional research include:
- Advancing theory and empirical evidence about the distributions of VTTS for populations and for major subgroups of travelers in different settings, including the distributions of VTTS for different types of commercial travel.
- Advancing theory and empirical evidence concerning variations in VTTS for particular individuals for different trip types and different travel situations. Included among considerations meriting attention is the potential non-linearity of VTTS with respect to the amount of time saved per trip (e.g., the value of 15 minutes saved is probably not 5 times the value of 3 minutes), and the need to distinguish the benefits of time savings due to operational improvements from the benefits of improved trip time reliability.
- Developing models and valid procedures for aggregating disaggregate information about VTTS distributions in order to provide accurate estimates of how the typical population traveling during a given time period in a given corridor or facility will respond to alternative pricing options, for example, pricing based on time-of-day and vehicle occupancies.
Clarifying how VTTS varies across populations and across the different trip types made by individuals, and its interplay with reliability, will allow planners to better estimate the potential use of toll facilities, including managed lanes and HOT lanes. Better information about these distributions will also contribute to increased understanding and improved methods for estimating the net societal benefits of these facilities – as the travelers choosing to use optional toll facilities often value their time savings very highly for the particular trips in question. It will also contribute to better understanding of how toll facilities provide congestion insurance to travelers who on occasion desperately need to travel quickly, where using an average VTTS greatly underestimates the value of this option.
A related issue revolves around the productive use of travel time, since in some cases, due to technologies available en route, travel time may no longer be “lost” to productive business. The standard example on this front is the use of laptops on trains and planes, where work can be done almost as from the workplace. More investigation is needed into the effect of this phenomenon on VTTS.
|Index Terms:||Travel time, Value of time, Transportation planning, Reliability, Travel behavior, High occupancy toll lanes, High occupancy vehicle lanes, Route choice, Travelers, Trip purpose, |