USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation
FHWA Highway Safety Programs

Permissive/Protected Left Turn Phasing in Detroit and Grand Rapids

Publication Year:

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 Datta
WSU-Transportation Research Group, MI
tdatta@eng.wayne.edu