Nebraska LTAP
Date of this Version
12-2018
Document Type
Article
Citation
Khattak, A. and Kang, Y. (2018). Offset right turn lanes, crash, design, two-way stop-controlled intersections, NDOT Research Report.
Abstract
This research focused on two aspects related to Offset Right Turn Lanes (ORTLs) on Nebraska state highway two-way stop-controlled intersections. The first was the crash safety and economic benefits of ORTLs compared to intersections with no right turn lanes or traditional right turn lanes. The second was driver stopping behavior at stop signs at two-way stop-controlled intersections equipped with ORTLs. The research team reviewed information from various published studies, analyzed crash data reported at 47 two-way stop-controlled intersections as well as collected and analyzed driver stopping behavior at six ORTLs in Nebraska. Traffic volume and reported crashes during 2012-2015 were statistically analyzed to assess safety effectiveness of three different types of right-turn lanes at two-way stop-controlled intersections. The three categories included intersections with ORTLs, no right turn lanes, and traditional right turn lanes. Cost-benefit analysis was conducted to ascertain viability of ORTLs. Driver stopping behavior on the intersection minor approaches (controlled by stop signs) at six intersections was examined to evaluate if drivers take advantage of the improved sight distance afforded by the ORTL at an intersection.
ORTLs had the lowest crash rates among the three intersection categories (intersections with ORTLs, no right turn lanes and traditional right turn lanes); however, the difference was statistically not significant. Average annual daily traffic was the only statistically significant factor related to crash frequency among these categories. The cost-benefit analysis indicated that compared to intersections with no right-turn lanes, ORTL intersections had an annual reduction of 0.202 crashes per million entering vehicles, which translates to $22,662 savings in crash costs per year. When compared with intersections having no right-turn lanes, a traditional right-turn lane reduced 0.0758 crashes per million entering vehicles annually or $8,504 savings in crash costs per year. Results of driver stopping behavior data analysis showed that number of through lanes, width of right-turn lane and width of the ORTL offset were statistically associated with driver’s stopping position on the minor approach and overall observed drivers were in good position to take advantage of the ORTLs improved sight distance.
In general, ORTLs have safety and economic benefits compared to two-way stop-controlled intersections with no right turn lanes and with traditional right-turn lanes. Given evidence that stopped drivers are in position to take advantage of improved sight distance afforded by ORTLs, they should be considered in the design/redesign of two-way stop-controlled intersections on priority basis. This recommendation is subject to site-specific conditions, which may vary considerably. Removal of right-turn lanes created from re-striped shoulders to intersections without right turn lanes is not recommended due to potential increase in crash rates.