The Value of Travel Time Reliability for Transit Passengers

This paper will discuss how the value of travel time reliability has been receiving increased attention the last few years. The paper presents results from a study that measured urban public transit passengers' valuation of travel time reliability. The main study covers three time periods (morning, mid-day and afternoon) and two transit modes (metro and commuter train). Two different choice experiments are used: one based on trade-offs of travel time, travel cost, arrival time and departure time, and one based on trade-offs of travel time, travel cost, delay risk and delay length. The first choice experiment allows for the calculation of the theoretical value of travel time reliability, given optimal choice of departure time. The second experiment allows for the arrival with a second valuation estimate that can then be compared with the first. If there is a difference between the two, various explanations can be tested, for example inherent risk aversion or significant non-linearities of scheduling delay costs. From the preliminary results of the pilot study (covering only the morning commute), the following can be noted: The valuation of risk p of a delay L is proportional to a function lying between the expected delay pL and the standard deviation of travel time. Theoretical results indicate that the valuation should be proportional to the expected delay, given a travel time distribution with two point masses (on time or a (p,L) delay), assuming free choice of departure time, homogeneous travelers and no inherent risk aversion. However, recent research on long-distance train passengers has indicated that the expected delay is not a good approximation of passengers’ actual valuation. Scheduling delay costs, as estimated from the scheduling choice experiment, seem comparatively small compared to the value of travel time. This implies a low value of travel time variability, assuming no inherent risk aversion. This is not consistent with the findings in the second experiment, where “later arrival than the current” were phrased as an unknown risk of being late compared to the planned arrival time, rather than a planned late arrival. This may be interpreted as inherent risk aversion, or that activities can in fact be comparatively easily rescheduled, provided that one knows the arrival time in advance. Values of travel time are essentially in line with what is found in “standard” value of time studies. This strengthens the validity of the choice experiment and also indicates that the usual values of travel time are probably free from a “hidden risk premium” in terms of travel time variability.