Indicators of Driver Adaptation to Forward Collision Warnings: A Naturalistic Driving Evaluation

Over the past decade, several studies have determined that vehicles equipped with forward collision warning (FCW) systems can help drivers reduce their likelihood of getting into a crash. To date, the research has only addressed the initial safety benefits incurred by drivers using FCW systems based on short-term exposure (up to one month), and not how those benefits may change over time with longer exposure. In this study, the performance, safety impact, and driver acceptance of a FCW system with automatic emergency braking (AEB) were assessed. Specifically, the project investigated how the safety impact of the system changed over time. This analysis is based on data collected during a one-year naturalistic field test in which 38 participants 20 to 29 years old drove 2013 Cadillac SRXs equipped with FCW and AEB systems. Participants were divided into three exposure groups, “short-term” (approximately 3 months), “medium-term” (approximately 9 months), and “long-term” (approximately 1 year). The accuracy of the alerts and AEB events were characterized by conducting detailed analysis of each event using in-house video analysis software. Detailed vehicle dynamics analyses were also conducted for each AEB event. To assess safety impact, two areas were addressed: overall driving behavior and rear-end near-crash events. Overall, both the observed accuracy and frequency of FCW alerts in the field test were very high, while the accuracy and frequency of AEB events was not. No changes were observed in driver’s speed maintenance, following headway, or alert rate (when alert sensitivity setting was accounted for). The analysis of driver’s exposure to near-crash events showed a statistically significant decrease in the number of near-crash events per mile, from a predicted 2.634 near-crashes per 1,000 vehicle miles traveled (VMT) during the first 1,000 miles to 0.615 conflicts per 1,000 VMT during the last 18,000 miles (a 76.6% decrease). In terms of changes in near crash exposure by time, drivers showed a statistically significant decrease in the number of near-crash events per month, from a predicted rate of 2.377 conflicts during the first month to 0.815 conflicts during the fourteenth month (a 65.7% decrease). These results suggest that the safety benefits of FCW systems are sustained over longer-term exposure.