Tolls Versus Mobility Permits: A Comparative Analysis

To address traffic congestion, two categories of instruments are used: price regulation (for instance, road pricing or congestion tolling) and quantity regulation (credit-based mobility schemes). Although the comparison of price and quantity regulation has received significant attention in the economics community, the literature is relatively sparse in the context of transportation systems. This paper develops a methodology to compare the toll and mobility permit instruments using a simple transportation network consisting of parallel highway routes and a public transport alternative. The permits can be traded across roads. The demand for each route is determined by a mixed logit route choice model and the supply consists of static congestion. The comparison is based on the optimum social welfare which is computed for each instrument by solving a non-convex optimization problem involving the mixed logit equilibrium constraints. Equity considerations are also examined. Numerical experiments conducted across a wide range of demand/supply inputs indicate that the toll and mobility permit instruments perform very closely in efficiency terms. The permit system is on average more efficient, but only by a small margin.