A novel mobility consumption theory for road user charging

Building on the analogy between electrical energy and mobility, we propose a novel mobility consumption theory based on the idea of the required reserved space headway of vehicles while driving. In this theory, mobility is "produced" by road infrastructure and is "consumed" by drivers in a similar fashion to power that is produced in power plants and consumed by electrical devices. The computation of mobility consumption only requires travel distance and travel time as input, as well as two physical parameters that are readily available, namely vehicle length and reaction time. We argue that mobility consumption is a more comprehensive measure for road use than travel distance (or travel time) alone as it captures road use over both space and time. One application area for our mobility consumption theory that we look at in this study is road user charging. We propose mobility consumption as the basis of a new charging scheme, which we refer to as mobility-based charging. Impacts of mobility-based charging and distance-based charging are compared in two case studies. When considering only departure time choice in a simple bottleneck model, we show that mobility-based charging can reduce congestion akin a congestion pricing scheme, unlike distance-based charging. Further, when considering route choice, we show that distance-based charging can increase congestion as it encourages drivers to take shortcuts through routes with low capacity, while mobility-based charging mitigates this effect. The proposed mobility-based charging scheme is further capable of considering technological innovation in vehicle automation and carbon charging.