Efficiency and Fairness of System-Optimal Routing with User Constraints

We study the route-guidance system proposed by Jahn, Mohring, Schulz, and Stier-Moses (2004) from a theoretical perspective. This method computes a traffic pattern that minimizes the total travel time subject to user constraints, which ensure that routes suggested to users are not much longer than shortest paths. We show that when distances are measured with respect to travel times at equilibrium, the resulting traffic assignment is efficient and fair.