Safety Impacts of Converting Two-Way Left-Turn Lanes to Raised Medians and Associated Design Concerns

Raised medians and two-way left-turn lanes (TWLTLs) are the two most common types of median treatments on arterial streets. The Florida Department of Transportation (FDOT) has had a policy to convert TWLTLs to raised medians since the early 1990's. This FDOT policy was based on earlier studies showing the benefits of raised medians over TWLTLs. However, some more recent studies have shown conflicting results. This paper aims to address this concern through a detailed study on the safety impacts of conversion from TWLTLs to raised medians. In addition, the study also investigated several potential safety concerns related to raised medians, including crashes at median openings, vehicles directly hitting the median curb, and median crossover crashes. Based on segment length and data availability, 18 urban arterial sections in Florida totaling 17.51 miles that were converted from TWLTLs to raised medians were analyzed. Police reports of all the crashes before and after median conversion were reviewed to correct miscoded crash types and obtain additional detailed crash information. Overall, the results showed a 30% reduction in total crash rate after median conversion. Six-lane facilities experienced a statistically significant reduction in total crash rate while four-lane facilities experienced a statistically insignificant reduction after the conversion. Among the four different types of median openings, uni-directional median opening was found to be the safest alternative to facilitate left-turning movements, and the full median opening with left-turn bays in both directions was found to be the least safe alternative to facilitate left-turning movements. Crashes involving vehicles hitting the curb and median crossovers were not found to be a serious safety concern. Crash data did not show evidence that raised medians provided additional hazard compared to TWLTLs.

• Supplemental Notes:
  • This paper was sponsored by TRB committee AHB65 Operational Effects of Geometrics.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Alluri, Priyanka
  • Gan, Albert
  • Haleem, Kirolos
• Conference:
  • Transportation Research Board 93rd Annual Meeting
  • Location: Washington DC
  • Date: 2014-1-12 to 2014-1-16
• Date: 2014

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; Photos; References; Tables;
• Pagination: 17p
• Monograph Title: TRB 93rd Annual Meeting Compendium of Papers

Subject/Index Terms

• TRT Terms: Arterial highways; Before and after studies; Crash rates; Highway design; Highway safety; Medians; Two way left turn lanes
• Identifier Terms: Florida Department of Transportation
• Subject Areas: Design; Highways; Operations and Traffic Management; Safety and Human Factors; I82: Accidents and Transport Infrastructure; I85: Safety Devices used in Transport Infrastructure;

Filing Info

• Accession Number: 01520271
• Record Type: Publication
• Report/Paper Numbers: 14-4799
• Files: TRIS, TRB, ATRI
• Created Date: Mar 27 2014 2:56PM