Strong Regularity and the Sensitivity Analysis of Traffic Equilibria: A Comment

Patriksson (2004) analyzes the sensitivity of solutions of traffic equilibrium problems. One of his central results deals with directional differentiability in the elastic-demand case. Unfortunately, his proof contains crucial errors, and the purpose of this comment is to explain what they are and why they render the proof incorrect. The consequence is that Patriksson’s proof of his Theorem 5 is invalid, so the theorem must be regarded as unproven.