| Ramp metering is a freeway onramp access control strategy to reduce freeway congestion. It consists of sensors such as inductive loop detectors to measure the density and flow of traffic on the freeway and control devices such as traffic lights on the ramps to limit the flow of vehicles entering the freeway. Empirical studies show that freeway delay can be reduced using ramp metering. Empirical evidence also shows that higher freeway traffic flows can be achieved by limiting the traffic flowing from freeway onramps. The practice of delaying access to freeway ramp users to improve traffic conditions for the freeway mainline users raises equity concerns.; This study uses a numerical example, a simulation and an empirical study to examine the effects of ramp metering strategies on the overall freeway system and on individual routes. The effect on the freeway system is measured by the total aggregated time of all users and the effect on the individual routes is measured by their own travel times. Individual route travel times serve as a measure of equity with respect to users of these routes. This study considers all users as a similar group (i.e., horizontal equity); it does not consider the income, gender or other social characteristics of users (i.e., vertical equity).; In the cases examined, the study finds that ramp metering reduces the total aggregated travel time of all vehicles on the system routes. Furthermore, it concludes that the reduction in travel time is not equally distributed among all the routes. In fact, in many cases, travel times are increased on some routes. This supports that ramp metering strategies cannot make substantial improvements in freeway throughput without inequitably affecting many onramp users. I conclude that travel demand tools such as congestion pricing, improved transit options, traveler information and smart parking incentives are needed to address the inequity created by ramp metering. |
