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

Authors

Jonathon Camenzind, University of Nebraska-LincolnFollow

First Advisor

Aemal Khattak

Date of this Version

Spring 5-4-2023

Citation

Camenzind, J. (2023). Safety and Operational Assessment of Rural Free Right-Turn Ramp Intersections [Master's thesis, University of Nebraska-Lincoln].

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Civil Engineering, Under the Supervision of Professor Aemal Khattak. Lincoln, Nebraska: May, 2023

Copyright © 2023 Jonathon Camenzind

Abstract

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 Khattak