How much traffic is too much? Finding the right vehicle quota for a scenic mountain road in the Italian Alps

An effective yet neglected option to limit the detrimental effects of car traffic in natural tourist destinations is the imposition of vehicle quotas. Defining the right quota for a road system, however, may not be straightforward because of the complex connection between the number of vehicles entering the system and traffic levels across space and over time. In this paper, we present a novel approach to tackle this issue that combines agent-based modeling and standards of quality, and we use it to define an hourly quota aimed at limiting traffic congestion and demand for parking along a scenic road in the Dolomites (Italian Alps). The model is designed and calibrated using geospatial and traffic data, and the acceptability of the quotas is further tested according to the hourly modal splits they might induce. Our model simulations highlight that, by redistributing morning traffic inflows, the quota can almost eliminate congestion with only a negligible impact on overall traffic figures. Further, while traffic reductions of up to 35% may be needed to eliminate traffic-related issues, more reasonable reductions (i.e. 10–25%) may be enough to address most of those. From an empirical perspective, the paper shows the effectiveness of quotas in sustainable transport and tourism; from a policy and management perspective, it proposes an approach for the definition of an ideal quota. The design of a quota system, however, requires detailed implementation and communication strategies, and more advanced simulation tools to capture circulation patterns induced by such strategies.