Why is steering not the same as braking? The impact of non-driving related tasks on lateral and longitudinal driver interventions during conditionally automated driving

With the ongoing trend towards conditional automation in the automotive industry, it is vital to ensure that drivers are able to resume vehicle control within the given time budget - even when engaging in non-driving related tasks. A driving simulator study was conducted to examine the impact of non-driving related tasks on drivers' ability to take over vehicle control. The task consisted of reading or proofreading a text (low vs. high visual cognitive task load) on a tablet which was either handheld or mounted in the vehicle (low vs. high manual task load). Data from 95 participants (mean age 38 years, 47 females) were used to examine reaction times and take-over quality in time-critical steering and braking maneuvers. Manual task load was found to prolong reaction times and to deteriorate take-over quality. Surprisingly, drivers needed even longer for the first gaze at the roadway when holding the tablet in their hands. As expected, these effects were stronger in the steering compared to the braking maneuver. Effects of cognitive task load were found to be dependent on the type of driver intervention. While reaction times and take-over quality deteriorated with increasing cognitive load in the steering maneuver, hardly any effects were found in the braking maneuver. A possible explanation for this surprising finding could be that especially drivers who are intensively engaging in non-driving related tasks spontaneously react with braking to defuse the situation and gain more time. It is thus argued that cognitively demanding non-driving related tasks during automated driving do not necessarily lead to deteriorated take-over performance. Depending on situational characteristics like the required reaction or the perceptual complexity of the situation, these might have different effects on the drivers' ability to take over. (C) 2017 Elsevier Ltd. All rights reserved.