Use of Level 1 and 2 driving automation on horizontal curves on interstates and freeways

June 2022

Introduction: Little is known about how the actual use of Level 1 and 2 driving automation systems may be affected by geometric road characteristics in naturalistic driving environments. This study examined the use of these systems on horizontal curves on interstates and freeways. Methods: We used travel data collected in a field operational test conducted with two 2016 Land Rover Range Rover Evoque vehicles equipped with adaptive cruise control (ACC) and two 2017 Volvo S90 vehicles equipped with ACC and Volvo's Pilot Assist. Logistic regression models estimated changes in the likelihood of ACC use associated with horizontal curvature in the Evoque vehicles, and of Pilot Assist and ACC use in the S90 vehicles, while accounting for traffic conditions. Results: Drivers were less likely to drive with ACC or Pilot Assist on as horizontal curves became sharper. In the Evoque vehicles, the likelihood of using ACC was 71.6% lower on the sharpest category of horizontal curves (those with a degree of curvature > 2.5 degrees per 100 feet of arc or a radius smaller than 2,292 feet), compared with straight road segments or the flattest horizontal curve category (those with a degree of curvature <= 1.5 degrees per 100 feet of arc or a radius no less than 3,820 feet). In the S90 vehicles, the likelihood of using Pilot Assist and ACC declined 74.6 and 66.3%, respectively, on the sharpest curves. Conclusions: Many driving automation systems face challenges on horizontal curves, even within their operational design domain. Future implementations that improve functionality may enhance driver experience and boost drivers’ confidence in these systems, which should increase their use and maximize the safety benefits these systems might offer.