Does cognitive distraction improve or degrade lane keeping performance? Analysis of time-to-line crossing safety margins

Studies on the effect of cognitive load (CL) on driving performance suggest that lane keeping performance is improved by cognitive distraction, due to a reduction in measures of the standard deviation of lateral position (SDLP). However, the effect of CL on drivers' lateral control is still not fully understood, and previous studies have shown mixed conclusions regarding the effect of CL on time-to-line crossing (TLC) safety margins. Hence, a driving simulator experiment was performed, requiring performance an auditory-response working memory task (CL task), during driving, presented at of three difficulty levels. Similar to previous studies, CL led to increased micro-steering activity, as well as a diminished SDLP, implying a better lane keeping performance. However, a systematic comparison of TLC calculations showed that the TLC values consistently decreased with the CL task, suggesting a degraded safety margin of lane keeping. While these decreased TLCs did not bring the vehicle close to actual lane departure, they do put into question the general finding that lane keeping is improved by cognitive distraction. We discuss how the increased micro-steering activity could lead to the somewhat counterintuitive simultaneous decrease in both SDLP and TLC. In addition, we suggest the use of a new method for TLC calculations, assuming constant lateral acceleration. We argue that by involving short time windows (3-5 s) of chunking, this method may be useful for assessing drivers' safety behavior, and correct detection of unsafe cognitive distraction.