Capacity-Allocation Methods for Reducing Urban Traffic Congestion

Abstract

It is unlikely that roadway construction or vehicle automation will be able to alleviate most major urban congestion in the near future (5–15 years). What else can be done to reasonably reduce congestion? Several approaches to reducing congestion by capacity allocation are reviewed: laissez-faire allocation, allocation by passenger load, ramp metering, road and parking pricing, allocation by trip purpose, rationing, and mixed strategies. These approaches are qualitatively compared against four criteria: effectiveness at reducing congestion, economic efficiency, income distribution effects, and flexibility of access for urgent trips. Recommendations are made regarding capacity-allocation measures with potential to reduce congestion and to increase economic efficiency. The equity impacts of these measures are identified and methods for mitigating these effects are proposed. Congestion pricing, together with free but metered on-ramps at freeways for nonpayers or with subsidies for lower-income households all are found to deserve further study and an incremental method of adoption is outlined.