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Effectiveness of All-Red Clearance Interval on Intersection Crashes

Status:  Complete
Report Date:  05/14/2004

Summary:

It is a widely-held assumption among traffic safety engineers (and the general public) that the addition of an all-red interval to the green-amber-red sequence significantly reduces the number of crashes at electronically controlled intersections. However, this assumption is based on statistics gathered in a relatively short period of time after the all-red interval is integrated into the traffic pattern. This research studies the short- and long-term safety benefits of the use of the all-red interval in the city of Minneapolis through the use of cross-sectional analysis, before-and-after analysis and statistical models comparing Minneapolis sites with and without an all-red clearance. Researchers employ data that reflects the number of crashes for an extended period of time after the introduction of the all-red interval. Much of this data shows that accident rates begin to rise after a period of adjustment on the part of drivers. The same drivers who are prone to "run" yellow lights are also prone to run red lights. The study also assesses the long-term benefits of the all-red interval in relation to the overall efficiency of traffic flow. Because widespread consensus seems to support the effectiveness of the all-red clearance interval as a safety measure--which may not be the case--the Local Road Research Board commissioned this research in response to a growing demand for increased mobility through more efficient signal timing.

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