Impact of Exit Ramp Enhancements on Traffic Operations and Safety: A Case Study of the I-81 Corridor

Abstract: This paper examines the intended and observed outcomes of an exit ramp enhancement along the I-81 corridor. Specifically, the extension of deceleration lanes and the addition of a turning lane at the exit ramp’s intersection were evaluated. The safety and operational measures of effectiveness studied in this paper helped identify the traffic growth percentage(s) that would result in a breakdown in traffic operations after the improvements were made. This was accomplished by recording and modeling field traffic data (pre-build and post-build) across multiple iterations of traffic growth and truck percentages. While the exit ramp improvements decreased queue lengths and the number of stops by 25 and 16 percent, respectively, the average delay did not significantly change two years after the enhancements were made. Projections were made beyond this period using validated microscopic models at traffic growths ranging from 12 percent to 32 percent. The most significant increase in delay, queue length, and the number of observed stops occurred at a 30% traffic increase. This indicates that prior to observing such growth, alternative measures should be considered. Using growth rate estimates, researchers were able to approximate the year in which such measures will be needed and provide suggestions to mitigate traffic at that time.