An Evaluation Scheme for Assessing the Effectiveness of Intersection Movement Assist (IMA) on Improving Traffic Safety

<b>Objective:</b> Intersection Movement Assist (IMA) has been recognized as one of the prominent countermeasures to reduce angle crashes at intersections, which constitute 22 percent of total crashes in the US. Utilizing vehicle-based sensors, vehicle-to-vehicle (V2░V), and vehicle-to-infrastructure (V2I) communications, IMA offers extended vision to provide early warning for an imminent crash. However, most of IMA related research implements their methods and strategies only in simulations, test tracks, or driving simulator studies that have quite a few assumptions and limitations, and hence the effectiveness evaluations reported may not be transferable or comparable. <b>Methods:</b> This study seeks to develop a generalized evaluation scheme that can be used not only to assess the effectiveness of IMA on improving traffic safety at intersections, but also to facilitate comparisons across similar studies. The proposed evaluation scheme utilizes the concepts of traffic conflict in terms of Time-to-collision (TTC) as a crash surrogate. This approach avoids the issue of having insufficient crash frequency data for system evaluation. To measure the effectiveness of IMA on reducing traffic conflicts, a relative risk is calculated for comparing the risk of with/without using the IMA. As a proof-of-concept study, this study applied the proposed evaluation scheme and reported the effectiveness of IMA on improving traffic safety in a Field Operation Test (FOT). Seven test scenarios were conducted at four intersections, and a total of 40 participants were recruited to use the IMA for six months. <b>Results:</b> It was estimated that IMA users have 26 percent fewer conflicts with TTC less than five seconds, and have 15 percent fewer conflicts with TTC less than four seconds. However, the results vary across different sites and different definitions of conflicts in terms of TTC. <b>Conclusions:</b> Overall, IMA is promising to effectively reduce angle crashes related to sight obstruction, and has potential to reduce not only crash frequency but also crash severity.