New Horizontal Equity Measure for Ramp Meters

Abstract

Ramp metering is a control technology used to manage the flow of traffic entering motorways and freeways, with the primary aim of minimizing congestion on the main thoroughfare. This technique has been studied and implemented globally since the 1960s. It has been shown that ramp meters improve the overall efficiency of the system; however, the distribution of the benefits and costs across users has been questioned, and this is one of the main constraints on user acceptance of the ramp metering system. The typical methodology used in the literature is to assume that the most equitable condition is when all on-ramps have the same delay across space or time. This research developed a new definition of horizontal equity for ramp meters and a proposed method for calculating it. A hypothetical microsimulation model was developed on the basis of a motorway in Sydney, Australia, and used as the platform to demonstrate how the proposed equity definition can be evaluated. To assist in the interpretation, two configurations of a ramp metering algorithm were simulated and compared. Finally, the typical equality measure used in the literature was calculated for the same scenarios and compared with the proposed equity measure. The results showed that these two measures can favor scenarios. A qualitative discussion of the expected benefits of the proposed equity measure is offered. Those expected benefits are an easy-to-communicate means of justifying the metering rates for user acceptance (rates that are arguably fairer, compared with the typical equality measure); a measure that is complementary to integration with other intelligent transportation system technology such as tolled bypass lanes; and ease of incorporation in the long-term traffic management plan.