Volume Warrant for Free Right-Turn Lanes at Unsignalized Intersections on Rural Two-Lane Highways

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Volume Warrant for Free Right-Turn Lanes at Unsignalized Intersections on Rural Two-Lane Highways

Mccoy, Patrick T. / Bonneson, James A.

The objective of the research presented in this paper was to develop a volume warrant for free right-turn (FRT) lanes at unsignalized intersections on rural two-lane highways. The warrant was based on a cost-benefit analysis that determined the right-turn volumes required to justify the construction and maintenance of FRT lanes at such locations. The research involved the evaluation of the safety and operational effects of FRT lanes. The safety effects of FRT lanes were determined from a comparison of the accident experience at intersections with and without FRT lanes. The operational effects of FRT lanes were analyzed using kinematic and traffic flow models. FRT lanes were not found to affect the frequency, severity, or types of accidents that occur at unsignalized intersections on rural two-lane highways. Thus, the benefits of FRT lanes are limited to improving the efficiency of right-turn movements. The results of the research indicate that design-year right-turn annual average daily traffic ranging from 440 to 825 vehicles per day, depending on the percentage of trucks, is required to warrant an FRT lane. A design speed of 64 km/h (40 mph) was found to be the most cost-effective design speed for FRT lanes. However, design speeds up to 89 km/h (55 mph) do not significantly reduce the cost effectiveness of an FRT lane.