Safety and Operational Analysis of Free Right-Turn Ramps at Rural Intersections

Abstract

This paper focuses on traffic safety and operational performance of rural, minor approach stop-controlled intersections with free right-turn (FRT) ramps. Studies on the guidelines, safety, and operational analysis of FRT ramps are limited. Therefore, this paper formulates a comprehensive framework of FRT ramp studies and applied it to Nebraska. The research compared 68 rural FRT ramp intersections with 24 similar non-FRT rural intersections to identify differences in crash frequencies, crash rates, and crash severity using 2010 to 2019 crash data from Nebraska Department of Transportation (DOT). The analysis did not show any statistically significant differences between the two intersection groups. Using a calibrated and validated microsimulation model, traffic operations at FRT ramp and non-FRT intersections were modeled and analyzed to study 324 scenarios, based on varying traffic and roadway geometry. Assuming a 20-year lifespan, using the operation data, cost–benefit analysis was conducted for combinations of discount rates (4%, 6%, 8%), major road annual average daily traffic (AADT) (5,000, 10,000, 15,000), minor road AADT (2,500, 5,000, 7,500), percentage of right-turning traffic (10%, 25%, 50%), FRT ramp radius (650, 1,200, 1,800 ft), and speed limit (45, 55, 65 mph). Using the results, this paper provides a guideline for Nebraska DOT for FRT ramp construction, reconstruction, or removal. Traffic agencies in Nebraska and the Midwest may make more informed decisions on FRT ramp based on guidance in this paper. However, the widely applicable methodology presented here to determine FRT ramp’s feasibility can be used in other locations in the United States without appreciable loss of generality.