Does automated driving affect time-to-collision judgments?

We compared time-to-collision (TTC) judgments between automated and manual driving to determine whether automation affected only responses (i.e., braking) or also affected visual perception (i.e., TTC estimation). Automation presumably frees cognitive resources because drivers do not have to control the vehicle. Those resources may be reallocated to processing visual information (e.g., optic flow) relevant for judgments of TTC. With a driving simulator, participants completed drives using manual or automated driving and responded to a rapidly decelerating vehicle using either the brake pedal or a button on the steering wheel (TTC judgment). They also completed a cognitive secondary task during half of the drives. Results suggest that automation can affect perceptual judgments (e.g., TTC estimation) in addition to driving responses (e.g., braking). TTC judgments were more accurate, and brake reaction times were faster, during automated driving than manual driving. This occurred even while performing a cognitively demanding secondary task, suggesting that participants used resources freed by automation to process visual information relevant to TTC judgments rather than complete non-driving tasks. TTC judgments were more accurate during automated driving than manual driving, presumably because automation freed up cognitive resources, allowing participants to assign those resources to processing of visual information (e.g., optic flow) relevant to judgments about collisions. To realize the safety benefit suggested by the results, automated systems should be designed so that cognitive resources freed by automation are assigned to information relevant to the driving task and not to non-driving tasks. (C) 2019 Elsevier Ltd. All rights reserved.