Choice of Routes in Congested Traffic Networks: Experimental Tests of the Braess Paradox

Abstract

The Braess paradox (Braess, 1968) consists of showing that, in equilibrium, adding a new link that connects two routes running between a common origin and common destination may raise the travel cost for each network user. We report the results of two experiments designed to study whether the paradox is behaviorally realized in two simulated traffic networks that differ from each other in their topology. Implementing a within-subjects design, both experiments include finite populations of paid participants in a computer-controlled setup who independently and repeatedly choose travel routes in one of two types of traffic networks, one without the added links and the other with the added links, to minimize their travel costs. Our results reject the hypothesis that the paradox is of marginal value and its force, if at all evident, diminishes with experience. Rather, they strongly support the alternative hypothesis that with experience in traversing the traffic network players converge to choosing the Pareto deficient equilibrium routes despite sustaining a sharp decline in their earnings.