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Center for Transportation Studies

Assessing the Safety Benefits of a Forward-Collision Warning System

Part of the Advanced Transportation Technologies Seminar Series — 2008 For more information, contact Shawn Haag at the ITS Institute, 612-625-5608 or

September 23

Hesham Rakha [bio]
Professor, Department of Civil Engineering, and Director, Center for Sustainable Mobility, Virginia Tech

Forward-collision warning (FCW) systems are designed to alert drivers to an impending rear-end (RE) crash. This may allow drivers to respond to a crash threat sooner, and thus reduce their impact speed or allow them to avoid a crash altogether. The presentation will describe a study that estimates the safety benefits of deploying a FCW system across the national fleet of heavy vehicles.

The approach in the study involved identifying RE conflicts within a heavy-vehicle naturalistic driving dataset using algorithms that identified potential RE events and removed non-threatening events. Since the heavy vehicles in this dataset were not equipped with FCW systems, the FCW auditory alarm severity and timing were introduced into the data using existing FCW system algorithms.

Driver perception-response times and braking levels to the computed FCW alarms were modeled using actual driver alarm-response behavior recorded in a previous heavy-vehicle FCW field operational test. Driver RE collision avoidance behavior—both with and without FCW alarm feedback—was then simulated using a Monte Carlo simulation approach. The simulation assumed that drivers selected the optimal braking response in the event that multiple FCW alarms were triggered.The number of conflicts avoided, as well as the additional response time available prior to encountering a crash, were then used to assess the safety benefits.

This study estimated that FCW systems may afford a 21 percent reduction in heavy-vehicle RE crashes, which translates to 4,800 crashes per year on U.S. highways.