The Prevalence of Paradoxes in Transportation Equilibrium Problems

Consider a congested transportation network, where the cost along each arc is affine, i.e., consists of a fixed cost plus a variable cost proportional to the flow. We present a new paradox demonstrating that, in a congested transportation network, a sufficiently high increase in the congestion effect along a route can result in the abandonment of a different route having the same origin and destination while the original route continues to be used. We also present a method for testing whether or not the paradox will occur in an arbitrary transportation network by viewing the question as a parametric linear complementarity problem. The new paradox is contrasted with Braess' paradox, and intuition is developed to explain the prevalence of such paradoxes in transportation equilibrium problems.