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                Permissive/Protected Left Turn Phasing in Detroit and Grand Rapids
**Publication Year:** 
            2010
    
        Original publication: Permissive/Protected Left Turn Phasing (FHWA-SA-09-015) (PDF, 441kB)

Left-turning movements are generally acknowledged to be the highest-risk movements at intersections. An estimated 27 percent of all intersection-related crashes in the United States are associated with left turns, with over two-thirds of these crashes occurring at signalized intersections (O'Connor, T., “Intersection Collision Avoidance Systems Web Page,” California Center for Innovative Transportation, August 2004). The cities of Detroit and Grand Rapids, Michigan, were concerned about the high number of crashes at some of their signalized intersections.

The cities modified the permissive left-turn mode to a permissive/protected mode at 3 intersections experiencing a high incidence of crashes, many with injuries and many due to left-turn head-on crashes.
"Two side-by-side photos of permissive-protected signal heads, with the photo on the left showing the permissive phase (circular green) and the photo on the right showing the protected phase (left-turn arrow)."Figure 1:   Permissive/Protected Mode*Photo courtesy of Michigan Department of Transportation (used with permission).*

Key Accomplishments

As the Michigan experience demonstrates, low-cost improvements can effectively improve safety and reduce traffic crashes and their resulting injuries.

Results

The enhanced countermeasure installed at these signalized intersections cumulatively reduced total crashes by approximately 32 percent, injury crashes by 58.9 percent, and left-turn head-on crashes by an average of 84 percent per year.

Contact

Tapan DattaWSU-Transportation Research Group, MItdatta@eng.wayne.edu U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

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