System-wide Safety Treatments and Design Guidance for 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 by developing guidance for 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.

VIEW REPORT

Report number: cmr 16-013
Published: June 2016
Project number: TR201510
Author(s): Dr. Praveen Edara (Principal PI), Dr. Carlos Sun (co-PI), Henry Brown (co-PI), Boris Claros, Zhongyuan Zhu  
Performing organizations: University of Missouri-Columbia Department of Civil & Environmental Engineering