TO: Board of Supervisors
FROM: Steven Lederer, Director of Public Works
REPORT BY: Syed Ahsan Kazmi, Senior Traffic Engineer, Public Works
SUBJECT: Napa County Left-Turn Lane Warrant/Screening Update
RECOMMENDATION
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Adoption of a Resolution updating the Napa County Left-Turn Lane Warrant/Screening Update (No Fiscal Impact).
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BACKGROUND
Napa County currently utilizes a left-turn lane warrant methodology to evaluate the need for left-turn lane installations at unsignalized intersections on the County roadway system. Left-turn lanes are an important roadway feature that can improve intersection operations, reduce vehicle delay, and enhance safety by separating turning vehicles from through traffic.
As traffic conditions, roadway safety considerations, and transportation engineering practices continue to evolve, the County periodically reviews its evaluation methodologies to ensure they remain technically sound, consistently applied, and aligned with current industry standards. Recent applications of the County's warrant methodology, together with advancements in national guidance related to left-turn lane operations and safety, provided an opportunity to assess the effectiveness of the existing criteria and determine whether updates were warranted.
To support this effort, Napa County retained Fehr & Peers to review the County's existing left-turn lane warrant methodology, evaluate current research and agency practices, and identify potential modifications or replacement criteria. The review included a comprehensive evaluation of national research and guidance documents, with particular emphasis on the National Cooperative Highway Research Program (NCHRP) Report 745, Guidance for the Design and Application of Shoulder and Turn Lanes on Two-Lane Rural Highways. NCHRP Report 745 represents the most current nationally recognized guidance for evaluating left-turn lane needs and is referenced by the American Association of State Highway and Transportation...
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