Assessing traveler compliance with the social optimum: A stated preference study

Abstract The development of Advanced Traveler Information Systems (ATIS) with en-route navigation systems has opened the door to new traffic regulation policies such as collective route guidance based on social costs, i.e. routes that minimize total travel time. However, a critical element for their efficiency is the compliance of travelers with route recommendations. It is well established that the social optimum is different from user equilibrium, where users drive on their shortest path. Thus, even when knowing that recommendations are for the common good, users may still choose not to follow the guidance given and drive as they wish. In this paper, we use a stated preference survey based on route choice situations from a real network to investigate traveler compliance for different levels of travel time sacrifice vs several social benefits. Two kinds of social benefits are considered: congestion alleviation and emission reduction. The data collected allows us to precisely quantify the travel time sacrifice that a given proportion of travelers would be ready to accept in order to take a different alternative that has a given level of social benefit. In line with the literature, our analysis confirms the decrease of compliance with the increase of sacrifice. Moreover, it suggests that the way the recommendation is intended could play a significant role in the level of compliance: the display of an advice message for the social path (in the congestion alleviation case) is shown to be more efficient than only showing additional information (in the emission reduction case).