Pigouvian road congestion pricing under autonomous driving mode choice

Abstract

Advanced autonomous vehicle technology is suggested to offer a unique solution to many of the current problems in road transport. This paper studies the impact of the transition in automated driving capabilities (driving mode choice) on road congestion pricing and vice versa, accounting for the interdependencies between traffic flow, the choice level of autonomous driving, effective road capacity and marginal travel cost. It is shown that (in a more or less distant future) when drivers can choose among various levels of car automation during a trip and when shortcomings associated with autonomous driving – e.g. adverse effects regarding privacy, software hacking, liability, safety, driving pleasure, manual control recovery – are non-negligible, their generalized user cost curve is the lower envelope of a swarm of traffic flow dependent individual cost curves whose slope is determined by the level of autonomous driving. This has several implications for our understanding of Pigouvian road congestion pricing. Most importantly, marginal social trip costs are then no longer convex and strictly increasing in traffic flow even when traffic is only ‘normally congested’, thereby introducing the possibility of multiple congestion pricing equilibria even in the absence of what is usually called ‘hypercongestion’. When inconveniences related to autonomous driving are sufficiently high, the imposition of congestion tolls may lead to a situation where drivers abandon autonomous technologies entirely and opt instead for fully manual driving. Our findings suggest that the emergence of advanced autonomous driving capabilities and the transition from manual to automated control on the road will probably make congestion pricing more, not less, complex for researchers and policymakers.