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Investigating the effect of urgency and modality of pedestrian alert warnings on driver acceptance and performance

Large, David R.; Kim, Hyungil; Merenda, Coleman; Leong, Samantha; Harvey, Catherine; Burnett, Gary; Gabbard, Joseph


Senior Research Fellow

Hyungil Kim

Coleman Merenda

Samantha Leong

Professor of Transport Human Factors

Joseph Gabbard


Hyungil Kim

Coleman Merenda

Samantha Leong

Joseph Gabbard


Active safety systems have the potential to reduce the risk to pedestrians by warning the driver and/or taking evasive action to reduce the effects of or avoid a collision. However, current systems are limited in the range of scenarios they can address using primary control interventions, and this arguably places more emphasis in some situations on warning the driver so that they can take appropriate action in response to pedestrian hazards. In a counterbalanced experimental design, we varied urgency (‘when’) based on the time-to-collision (TTC) at which the warning was presented (with associated false-positive alarms, but no false negatives, or ‘misses’), and modality (‘how’) by presenting warnings using audio-only and audio combined with visual alerts presented on a HUD. Results from 24 experienced drivers, who negotiated an urban scenario during twelve 6.0-minute drives in a medium-fidelity driving simulator, showed that all warnings were generally rated ‘positively’ (using recognised subjective ‘acceptance’ scales), although acceptance was lower when warnings were delivered at the shortest (2.0s) TTC. In addition, drivers indicated higher confidence in combined audio and visual warnings in all situations. Performance (based on safety margins associated with critical events) varied significantly between warning onset times, with drivers first fixating their gaze on the hazard, taking their foot off the accelerator, applying their foot on the brake, and ultimately bringing the car to a stop further from the pedestrian when warnings were presented at the longest (5.0s) TTC. In addition, drivers applied the brake further from the pedestrian when combined audio and HUD warnings were provided (compared to audio-only), but only at 5.0s TTC. Overall, the study indicates a greater margin of safety associated with the provision of earlier warnings, with no apparent detriment to acceptance, despite relatively high false alarm rates at longer TTCs. Also, that drivers feel more confident with a warning system present, especially when it incorporates auditory and visual elements, even though the visual cue does not necessarily improve hazard localisation or driving performance beyond the advantages offered by auditory alerts alone. Findings are discussed in the context of the design, evaluation and acceptance of active safety systems.


Large, D. R., Kim, H., Merenda, C., Leong, S., Harvey, C., Burnett, G., & Gabbard, J. (2019). Investigating the effect of urgency and modality of pedestrian alert warnings on driver acceptance and performance. Transportation Research Part F: Traffic Psychology and Behaviour, 60, 11-24.

Journal Article Type Article
Acceptance Date Sep 30, 2018
Online Publication Date Oct 18, 2018
Publication Date Jan 1, 2019
Deposit Date Nov 22, 2018
Publicly Available Date Oct 19, 2019
Journal Transportation Research Part F: Traffic Psychology and Behaviour
Print ISSN 1369-8478
Electronic ISSN 1879-2340
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 60
Pages 11-24
Keywords Urgency; Modality; Driver accceptance; Pedestrian alert systems
Public URL
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