Pilot Study Tested Adaptive Cruise Control Technology with Nine Test Speeds Ranging From 25 to 65 MPH in Virginia and Washington D.C.
Preferred Following Distance as a Function of Speed—Function-Specific Automation (Level 1) Applications
The gap distances used in Adaptive Cruise Control (ACC) and Cooperative Adaptive Cruise Control (CACC) systems are known to facilitate both driver and traffic safety. The objective of this study was to develop time gap curves that described comfortable and minimally acceptable following distances over a range of speeds, both with and without ACC engaged, through driving experiments conducted with 24 participants from the Washington, D.C. metropolitan area (including the U.S. DOT’s Turner-Fairbank Highway Research Center in McLean, Virginia), both before and after COVID-19. A questionnaire was collected after the drive, asking drivers about their familiarity with ACC, the experimental route, their driving experience, and driving frequency.
In this study, the survey participants drove an experimental course that included nine test speeds ranging from 25 to 65 mph, once using ACC and once while driving manually. For each of the nine test speeds, comfortable and minimally safe following gaps were recorded as the participants drove manually. The participants also rated their comfort with the ACC gap distance at the same locations and speeds. This way, a set of comfortable and minimally safe following gap curves were generated and compared to the gap distance curve of an existing ACC system in the market.
- Nearly 80 percent of the drivers were consistently comfortable with the gap provided by ACC across a range of speeds, with a minor drop in comfort levels around 45 mph.
- Even at 45 mph, when the proportion of survey participants who rated the ACC’s gap distance as comfortable was the lowest, more than half (56 percent) of the participants felt comfortable with the speed assigned by ACC.