Browse Publications Technical Papers 2021-01-0898

Drivers’ Responses to Lead Vehicles: Thresholds for Triggering an Emergency Response, Age Differences, Crash Risks, and Influence of Secondary Task Engagement 2021-01-0898

Analyses of driver response time studies and fatal crash statistics were examined to determine: 1. whether all rear-end crash types can be analyzed as one crash type, 2. average braking thresholds for drivers, and 3. the influence cell phone usage has on drivers’ response times when responding to a lead vehicle. The goal of this research is to recommend protocols for investigating LV crashes that is supported by the literature.
Two distinct lead vehicle [LV] response time events emerged: LV platoon (two vehicles traveling together in close proximity) and LV looming (a vehicle approaching a stopped or much slower LV). In normal driving, platoon LV events were very common but resulted in very few crashes per exposure. Young drivers were over-represented when they did occur. Onset of the hazardous event was when the LV decelerated, and drivers began braking roughly 3 to 5 seconds before impact. These results were consistent with the braking thresholds by naturalistic drivers in congested traffic, as well as the GM-Ford Crash Avoidance Metrics Partnership [CAMP] test-track research.
Conversely, LV looming crashes were rare, had much greater crash risk, involved drivers of all ages, and accounted for most fatal rear-end crashes. In this type of crash, drivers typically applied the brake less than 1.4 seconds before impact. These results were consistent with the braking thresholds by naturalistic drivers in smooth traffic and was nearly 3 times later than the braking thresholds by the 77th and 85th percentile responders in the CAMP tests.
Hands-free and hand-held calling was not associated with an increase in brake response times when responding to a lead vehicle. However, visual and manual tasks, such as texting and dialing caused drivers to respond slower than approximately 93% of other drivers when responding to a lead vehicle. Based upon these results, a refined definition of driver distraction was offered.


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