Determining Guidelines for Ramp and Interchange Spacing

This project considered the effects of geometry, traffic operations, safety, signing, and other factors to develop guidelines for understanding the considerations that influence minimum ramp and interchange spacing values. Phase I included conducting a literature search and other information gathering activities, developing a work plan to assess the impact of ramp spacing on traffic operations and safety, and developing a framework for the research guidelines. Phase II included creating microscopic simulation models of closely-spaced ramp combinations calibrated with field data, constructing a crash database and developing crash prediction models, developing a set of guidelines for ramp and interchange spacing, and recommending changes to major resource documents within the transportation profession. As a final product, the team wrote NCHRP Report 687, "Guidelines for Ramp and Interchange Spacing," to assist users as they consider new or modified ramps and interchanges.