Safety Effects of Using Short Left-Turn Lanes at Unsignalized Median Openings

The AASHTO Green Book specifically encourages the use of left-turn lanes at median openings on divided roadways to eliminate stopping in through-traffic lanes. However, the lengths for median left-turn lanes recommended by the Green Book are often impractical in urban areas, where the available distance between two adjacent openings is inadequate, and particularly where the volume of left-turning traffic is heavy. Thus, left-turn lanes shorter than the lengths recommended by the Green Book (referred to as short left-turn lanes) are in wide use on urban divided roadways. The objective of this study was to investigate the safety performance of short left-turn lanes at unsignalized median openings. To this end, 6 years of crash data were collected in Houston, Texas, from 52 median left-turn lanes (40 short lanes and 12 lanes with lengths in compliance with Green Book recommendations). A Poisson regression model was developed to relate traffic and geometric attributes to the total number of rear-end, sideswipe, and object–motor vehicle crashes in a left-turn lane. Crash modification factors were calculated for applications to project the crash frequency for a specific change in lane length. Statistical evidence indicates that the difference between actual lane length and Green Book–recommended length has significant effects on crash frequency. However, the increase in crash frequency as a result of short left-turn lanes might be acceptable in cases where engineers must account for traffic and economic and social effects in determining whether a short left-turn lane is appropriate.

• Record URL:
  https://doi.org/10.3141/2436-02
• Availability:
  • Find a library where document is available. Order URL: http://www.trb.org/Main/Blurbs/171937.aspx
• Authors:
  • Chen, Xiaoming
  • Qi, Yi
  • Lu, Yan
• Publication Date: 2014

Language

• English

Media Info

• Media Type: Print
• Features: Figures; Maps; References; Tables;
• Pagination: pp 13–22
• Monograph Title: Highway Design 2014, Volume 1
• Serial:
  • Transportation Research Record: Journal of the Transportation Research Board
  • Issue Number: 2436
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Crash data; Crash modification factors; Crash rates; Divided highways; Highway safety; Left turn lanes; Length; Median openings; Unsignalized intersections; Urban areas
• Identifier Terms: AASHTO Green Book
• Geographic Terms: Houston (Texas)
• Subject Areas: Design; Highways; Safety and Human Factors; I20: Design and Planning of Transport Infrastructure; I81: Accident Statistics;

Filing Info

• Accession Number: 01514502
• Record Type: Publication
• ISBN: 9780309295345
• Report/Paper Numbers: 14-0549
• Files: TRIS, TRB, ATRI
• Created Date: Feb 18 2014 5:21PM