Safety Effect of Intersection Signalization - A Before-After Study

Søren Underlien Jensen. Paper from TRB Annual Meeting 2010

This paper presents a before-after crash and injury study of intersection signalization in an urban area.

Conversion from yield to signal control at 54 intersections in central Copenhagen, Denmark, is analyzed. Police recorded crashes, which occurred at converted intersections as well as crashes up to 500 meters away on roadways leading up to converted intersections, are included in the study.

The method used accounts for general crash and injury trends, changes in traffic volumes, and also regression-to-the-mean effects in the before periode. The best estimates for mean safety effects of intersection signalization are decreases in crashes and injuries of espectively 21 and 17 percent at 3-armed intersections, and 39 and 33 percent at 4-armed intersections.

These findings are in line with previous studies. The safety benefits at converted intersections are primarily due to significant reductions in right-angle crashes.

Safety is also improved on roadways up to 100 meters away from the center of the converted 3-armed intersections, and up to 200 meters away from converted 4-armed intersections.

About 60 percent of the total safety improvement occurred on the roadways and only about 40 percent occurred at the converted intersections.

In total, for converted intersections and roadways up to 200 meters away, the best estimates for mean safety effects of intersection signalization are decreases in crashes and injuries of respectively 19 and 21 percent near and at the 3-armed intersections, and 26 and 33 percent near and at the 4-armed intersections.

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