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.

TRB's National Cooperative Highway Research Program (NCHRP) Report 687: Guidelines for Ramp and Interchange Spacing explores guidelines for ramp and interchange spacing based on design, operations, safety, and signing considerations. The report is designed to help aid the decision-making process when an agency is considering new ramps or interchanges on existing facilities, modifying ramps and interchanges of existing facilities, or when planning and designing new highway and interchange facilities. The guidelines also offer standardized definitions measuring ramp and interchange spacing, which have varied in previous design guides. A final report documenting the full research effort related to the development of NCHRP Report 687 was published as NCHRP Web-Only Document 169--

A reference work offering information on the basic principles and the proven techniques of traffic engineering.