Development of Left-Turn Lane Warrants for Unsignalized Intersections

• Published by:  Texas Transportation Institute

NCHRP Project 03-91,“Development of Left-Turn Lane Warrants for Unsignalized Intersections”, Active TRB Project
Researchers at the Texas Transportation Institute (TTI) recently completed NCHRP Project 03-91. Though the report has not yet been published, the draft final report (dated November 2010) has been provided to the AMM2 project team to review for this effort. The project effort included a literature review, key interviews, a legal review, and a driver behavior observational study. The researchers used field data to assess the various analytical procedures available for identifying left-turn lane needs. The researchers updated assumptions previously used in the Harmelink procedures and contrasted these findings to those from their own assessment. Ultimately, the TTI team recommended that the Harmelink approach may no longer be optimal and suggested the use of an economic analysis technique that includes an operations (simulation) component as well as evaluation of crash costs, crash reductions, and construction costs. Appendix B of their report includes recommended revisions to the AMM based on their new economic procedure.