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原文传递 System-wide Safety Treatments and Design Guidance for J-Turns.

题名：	System-wide Safety Treatments and Design Guidance for J-Turns.
作者：	Edara, P.; Sun, C.; Brown, H.; Claros, B.; Zhu, Z.
关键词：	Design guidance, Crash review, Implementation, Effectiveness analysis, Rural highways, Acceleration lanes, U-Turns(Roads), Signal control enhancement, J-turns, Rear-end crashes, Missouri Department of Transportation (MoDOT)
摘要：	In an effort Toward Zero Deaths (TZD) the Missouri Department of Transportation (MoDOT) initiated this research project to develop guidance on treatments that can reduce crashes and fatalities. The project first synthesized the literature and state of practice on system-wide safety treatments and documented their effectiveness. In particular, the objective was to examine those treatments that have not been already implemented in Missouri. The safety effectiveness, implementation guidelines, limitations, costs, and concerns of the treatments were documented. The identified safety treatments work in conjunction with the ‘Necessary Nine’ strategies identified in the Missouri’s Blueprint. Accordingly, the synthesis covered three areas: 1) Horizontal curves, 2) Intersections, and 3) Wrong way crashes. The reviewed treatments included signing, geometric and access management, ITS, pavement markings, and signal control enhancements to improve safety. In the last few years, MoDOT has replaced several high crash intersections on rural highways in the state with J-turns. Given their safety effectiveness and low cost the J-turn has become a preferred alternative to replace high crash two-way stop-controlled intersections on high speed highways. Unfortunately, national guidance on the design of J-turns is very limited. This project addresses this gap in practice by developing guidance on spacing and acceleration lanes. A thorough examination of crashes that occurred at twelve existing J-turn sites in Missouri was conducted. The crash review revealed the proportions of five crash types occurring at J-turn sites: 1) major road sideswipe (31.6%), 2) major road rear-end (28.1%), 3) minor road rear-end (15.8%), 4) loss of control (14%), and 5) merging from U-turn (10.5%). The crash rates decreased with the increase in the spacing to the U-turn, for both sideswipe and rear-end crashes; J-turns with a spacing of 1500 feet or greater experienced the lowest crash rates. A calibrated simulation model was used to study various volume scenarios and design variables. For all scenarios, the presence of acceleration lane resulted in significantly fewer conflicts. Thus, acceleration lanes were recommended for all J-turn designs, including lower volume sites. Second, while spacing between 1000 feet and 2000 feet was found to be sufficient for low volume combinations, spacing of 2000 feet was recommended for medium to high volume conditions.
总页数：	Edara, P.; Sun, C.; Brown, H.; Claros, B.; Zhu, Z.
报告类型：	科技报告