Freeway ramp metering systems are being used to alleviate urban freeway congestion. This report presents a methodology for determining the distance requirements for ramp metering for a wide range of traffic volume and freeway geometric conditions. The distance requirement for ramp metering consists of distance required queue storage and distance required for the freeway merging operation. A queue storage model has been developed to determine distance required for queue storage. The constant acceleration models of linear motion have been used to determine distance required for the freeway merging operation. A methodology for determining the optimal placement of the ramp meter signal has been presented. Guidelines for effecting a trade-off between queue storage an freeway merging distance requirements have also been presented. A sample problem demonstrates the use of the presented methodology.

Ramp metering is an effective, viable, and practical strategy used to manage freeway traffic. It is a proven freeway management technique as various forms of ramp control have been in place since the 1960s in the Chicago, Detroit, and Los Angeles areas. Due in part to the success of these early applications, ramp metering has received increased emphasis in recent years under the umbrella of advanced traffic management systems (ATMS), a component of intelligent transportation systems (ITS). ITS America reports that there are currently more than 40 ATMS deployed, under construction, or in the planning stage in the U.S. by state transportation agencies. The future of ramp metering is also in this ITS context. Integration and interface with local street system control and other advanced ITS traffic control systems such as advanced vehicle control systems, dynamic route guidance, and advanced traveler information systems are the latest in ramp metering applications. Ramp meters are in place and working effectively on segments of I-395 and I-66 in Northern Virginia. The Virginia Department of Transportation is very much interested in the feasibility of implementing ramp metering on other segments of freeways throughout the state. Accordingly, the purpose of this study was to review and synthesize the existing literature on ramp metering. Specific topics included in the review were: impacts of ramp metering, including its advantages/benefits and disadvantages/disbenefits, warrants, criteria, and guidelines for ramp metering, metering rates. Detailed information on these topics is included in the report as well as general conclusions regarding ramp metering.