Effects of User Interface Assertiveness on Acute Stress and Performance in a Takeover Request


  • Vanessa Kraut University of Vienna



While intense warnings can be lifesaving for drivers by evoking fast responses, they may startle them and lead to dangerous braking behavior [1]. In automated vehicles, the management of mental stress is decisive for safe takeovers. Drivers may experience mental underload when automation is activated but are expected to safely navigate critical situations after a takeover request. Excessive acute stress decreases their ability to assess the situation, resulting in worse driving performance [2]. While assertive signals are thought to be more effective at evoking immediate response, resuming full control over the vehicle can take up to forty seconds [3]. It is unknown if the initial effectiveness of assertive signals might be offset by the increased stress response.


We will evaluate assertiveness levels of abstract auditory takeover requests in a pilot study. In addition, the performance measures to be included in the main study will be selected. Possible variables include distance to collision, steering wheel variability, braking reaction time, lateral control as well as traffic rule compliance [1], [3]. The main study will be using a between-subject design, in which subjects will drive a conditionally automated car in a simulator and receive high or low assertive takeover requests. Dependent variables include driving performance and the physiological measure of stress, assessed via heart rate variability which strongly correlates with mental stress [2]. For each takeover, subjects will also rate their perceived stress level.

Expected Results

The results will model how the stress response and driving performance evolve from the takeover request to the driver resuming full control of the vehicle. Previous findings suggest that high assertive warnings are expected to result in a longer distance to collision and faster braking and steering reactions [1]. Overall, high assertive signals will result in worse lateral performance, higher stress ratings and lower heart rate variability, indicating increased mental stress. Ultimately, these insights can inform the design of a takeover system, that mitigates the effects of suboptimal mental driver state on road safety and user experience [2].


[1] E. Pakdamanian, N. Namaky, S. Sheng, I. Kim, J. A. Coan, and L. Feng, „Toward Minimum Startle After Take-Over Request: A Preliminary Study of Physiological Data“, in 12th International Conference on AutoUI Virtual Event DC USA, Sep. 2020, S. 27–29.

[2] S. Agrawal and S. Peeta, „Evaluating the impacts of driver’s pre-warning cognitive state on takeover performance under conditional automation“, Transp. Res. Part F Traffic Psychol. Behav., Bd. 83, S. 80–98, Nov. 2021.

[3] N. Merat, A. H. Jamson, F. C. H. Lai, M. Daly, and O. M. J. Carsten, „Transition to manual: Driver behaviour when resuming control from a highly automated vehicle“, Transp. Res. Part F Traffic Psychol. Behav., Bd. 27, S. 274–282, Nov. 2014.