Assessment of Dynamic Speed Limit Management on Metropolitan Freeways

This article evaluates the impacts of dynamic speed limit strategies in metropolitan freeways. An objective function is defined in order to balance the benefits (e.g., reduction of congestion, pollutant emissions and fuel consumption, or increase in traffic safety) and costs (e.g., increase of free flow travel times). This function is generic in its nature, and could be used to assess any type of traffic management strategy. In particular, it is applied to the Barcelona's freeways dynamic speed limit management case study. The results suggest that the social profitability of dynamic speed limit (DSL) management in metropolitan freeways is limited. The main reason for this is the reduced effect of this kind of policy, if isolated in application, in alleviating congestion. It is emphasized that the absolute magnitude of the profitability is highly sensitive to the value given to each one of the social costs. The profitability of the policy would improve if the value of traffic externalities increased in relation to the marginal cost of travel times. A sensitivity analysis with respect to this last cost is presented. The potential synergies of applying DSL strategies jointly with other active traffic management policies should be considered as an issue for further research.