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The Minnesota Department of Transportation (MnDOT) is investing significant resources in intersection collision warning systems (ICWS) based on early indications of effectiveness. However; the effectiveness is not well documented; and negative changes in driver behavior at treatment intersections may affect drivers overall; resulting in a spillover effect. Moreover; the effectiveness of ICWS may decrease if drivers do not perceive a change in the dynamic messages. Therefore; the objectives of this research were to (1) evaluate driver behavior at mainline and stop-controlled approaches for intersections with and without ICWS and (2) assess the traffic volume range and limits where the system is nearly continuously activated and is likely to lose its effectiveness. Video data were collected at five treatment and corresponding control intersections; and various metrics were used to compare changes in driver behavior. In general; no negative behaviors were noted for either treatment or control intersections.

This study is a complement to Evaluation of Intersection Collision Warning Systems in Minnesota (2017-38), which was published in October 2017. That project evaluated behaviors such as type of stop for drivers on the minor approach in the presence of intersection collision warning systems (ICWS). This project was a follow-up to that study and compared speeds along the major street approaches at ICWS treatment sites after installation of the system to determine whether the ICWS provided any measurable impact on speed when drivers on the major street were presented with a message from the system (activated) versus when drivers were not presented with a message (not activated). The study found that mean and 85th percentile speeds were lower on the major approach when the ICWS was activated compared to when it was not activated. However, the differences were minor. As a result, the system is expected to reduce speeds, but only a modest impact is expected in terms of mainline drivers.