Safety and Operational Assessment of Rural Free Right-Turn Ramp Intersections

Free right-turn (FRT) ramps are alternative right-turn lane designs for intersecting highways. As of 2023, 79 FRT ramps exist at 68 rural highway intersections in Nebraska. FRT ramps may be located on three-legged or four-legged intersections and may be on the minor, the major, or both minor and major approaches of the same intersection. This research compared the 68 rural FRT intersections to 24 similar non-FRT rural intersections to identify differences in crash frequency and crash rate and tested for statistical significance using a two-sample t-test. Crash data were obtained for the ten- year period of 2010-2019, with a focus on crashes reported within a quarter mile of each intersection leg. Forty different comparisons were made between the FRT and non-FRT intersections, testing varying intersection legs, AADT, and location of the FRT ramp on the major, minor, or both approaches. The results of this analysis indicated a lack of any statistically significant difference in crash frequency or crash rate among the rural FRT ramp and rural non-FRT intersections. In addition to the safety analysis, a conflict analysis was conducted to analyze the vehicle interactions between right-turning vehicles at the FRT ramp intersections and non-FRT intersections. Miovision Scout video recording equipment was used to record the traffic conflicts over 72 hours at six FRT intersections of varying AADT and the number of intersection legs. Six non-FRT intersections were paired with the FRT intersections and the conflict experienced by right-turn movement on the same approach as its FRT counterpart was observed. The conflict analysis showed that non-FRT right- turns experienced higher conflicts per 1000 entering right-turning vehicles than the FRT ramp intersections. It was concluded that the presence of FRT ramps at rural intersections does not affect the crash frequency or crash rate experienced. It was also concluded that conflict is reduced between right-turning vehicles and other traffic present at the intersection when an FRT ramp is present, especially compared to non-FRT intersections where no exclusive right-turn lane is present on the major approach. It is recommended that future research assess additional operational benefits of FRT ramps, such as delay and travel time. Advisor: Aemal Khatta

Inventory, Operations, and Safety at Free Right-Turn Ramps

SPR-FY22(012)This research focused on traffic safety and operational performance of rural, minor approach stop-controlled intersections with free right-turn (FRT) ramps. The objectives of the research were to: \u2022 Create a statewide inventory of rural FRT ramp intersections and provide to the Nebraska Department of Transportation (NDOT), \u2022 Using NDOT 10-year crash data, conduct statistical safety analysis of rural FRT intersections extending \ubc-mile in each direction from the intersection, \u2022 Study vehicular operations at rural intersections with and without FRT ramps including a comparison of vehicular conflicts, and \u2022 Develop guidelines for operations and safety tradeoffs to assist with NDOT projects on maintaining similar locations, removing, or reconstructing ramps. As of 2023, 79 FRT ramps exist at 68 rural highway intersections in Nebraska. FRT ramps may be located on three-legged or four-legged intersections and may be on the minor, the major, or both minor and major approaches of the same intersection. The research compared the 68 rural FRT ramp intersections to 24 similar non-FRT rural intersections to identify differences in crash frequencies, crash rates, and crash severity using 2010-2019 crash data from NDOT. The analysis did not show any statistically significant differences between the two intersection groups. This result is identical to a 1995 Nebraska-based study of rural FRT ramp intersection safety. The research investigated vehicular conflicts between right-turning vehicles by pairing six non-FRT intersections with six FRT ramp intersections and collecting data using video recording equipment. The comparison was between vehicular conflicts experienced by right turning traffic on the same approach of the FRT ramp and non-FRT intersections. Data analysis showed that non-FRT right-turns on the minor approach, major approach with no exclusive right-turn lane, and major approach with an exclusive right-turn lane experienced statistically significantly higher conflicts per 1,000 entering right-turning vehicles than FRT ramp intersections. A VISSIM microsimulation model of traffic operations at FRT ramp intersections and non-FRT intersections enabled the creation of 324 scenarios, based on varying traffic and roadway geometry. Assuming a 20-year lifespan, benefit cost (B/C) analysis was conducted for combinations of discount rates (4%, 6%, and 8%), major road AADT (5,000; 10,000; 15,000), minor road AADT (2,500; 5,000; 7,500), percent right turning traffic (10%, 25%, 50%), FRT ramp radius in feet (650; 1,200; 1,800) and speed limit in mph (45, 55, 65). Traffic operational benefits are the basis for considering FRT ramp construction, reconstruction, or removal at rural, minor approach stop controlled intersections in Nebraska. The reason is the absence of any discernable differences in safety at FRT ramp and comparable non- FRT intersections. NDOT can make more informed decisions on FRT ramp intersections based on guidance in this report