Illusion of Motion Variation in Value of Travel Time Under Different Freeway Driving Conditions

have used either revealed preference or stated preference data and various forms of logit choice models (e.g., multinomial, nested, and mixed random effect) to identify marginal rates of substitution between travel time and the price of a trip. It is intuitive that the value of travel time is not constant in all situations. Previous studies suggest it varies by assorted trip characteristics including journey purpose, length, mode, sign and size of time savings, and personal attributes such as income, although the studies were done with different degrees of rigor and some findings were inconclusive. The literature on value of travel time is vast, but the part of that literature that focuses on differentiating travel time by the quality of the trip is almost nonexistent. The mode choice literature has thoroughly distinguished and assessed values of in-vehicle and out-of-vehicle (access and wait) transit times (1), but similar analysis on the highway side is very recent. An experiment by Hensher distinguished between free-flow time, slowed-down time, and stopand-go time (2). Little research specifically concerns how ramp metering and highway congestion affect driver perceptions in terms of time, frustration, and annoyance. A better understanding of such effects promises improvements in the design and evaluation of freeway traffic control strategies. A recent empirical study using data from both a traditional stated preference survey and driving simulation further estimated the driver acceptance of the qualitatively dissimilar in-vehicle travel experiences of waiting at a ramp meter, driving in free-flow traffic, and driving in congested traffic (3, 4). In their experiment, the drivers’ preferences to ramp wait (up to 6 min) and various freeway mainline travel conditions were elicited in several sets of choice conditions. The findings, though inconclusive, indicate that people may perceive ramp wait and freeway travel differently. An important issue ignored in previous studies is whether the weight drivers put on ramp delay in relation to freeway travel increases with the length of ramp delay. In other words, drivers may perceive each additional minute of delay as more onerous than the previous minute. Zhang and Levinson demonstrated that, if this hypothesis were true, the traditional freeway control objective of minimizing total travel time would not be consistent with utility maximization (5). Moreover, if a weighting function for all lengths of ramp delay is quantified, it will become possible to implement a more desirable freeway control objective, that is, minimizing perceived travel time. This study uses a larger data set involving longer ramp delays (up to 18 min) than reported by Levinson et al. (3), both of which are generated in the same computer-administered stated preference survey. Unlike previous studies, which assumed a constant value of time for each specific driving situation, this research relates the perception and satisfaction of trip quality to the length of ramp wait. A nonlinear weighting function for ramp wait derived from the findIllusion of Motion Variation in Value of Travel Time Under Different Freeway Driving Conditions