The impact of rear-view mirror distance and curvature on judgements relevant to road safety

Abstract

We report two experiments that investigate the impact of rear-view mirror distance and curvature on distance, spacing, and time-to-contact (TTC) judgements. The variation in mirror distance had a significant effect on TTC judgements, but only marginally influenced distance and spacing estimations. As mirror distance increased, TTC was overestimated, which is potentially dangerous. Control conditions with identical visual angles across different mirror distances revealed that effects were not solely caused by variation in visual angle. The impact of mirror curvature moderated the effect. While observers were unable to compensate for the mirror distance effect, they could do so for the distortions generated by non-planar mirrors, at least up to a certain degree of distortion. Implications for vehicle design and national guidelines are discussed.

Practitioner Summary: Regulations regarding rear-view mirrors are vastly different between countries. For instance EU regulations encourage convex driver-side mirrors, whereas US regulations allow them merely on the passenger's side. The use of a dynamic TTC paradigm puts the human factors designer in a position to evaluate the existing regulations and to design safer mirrors.

Keywords:

• rear-view mirror
• mirror distance
• mirror curvature
• time-to-contact
• visual angle

Acknowledgements

We are grateful to Franziska Baldauf and Tanja Dörfler for assisting with data collection and to Agnes Münch for programming the TTC simulation. André Dittrich kindly made the contact to the local car dealership and enabled the preliminary examination. Finally, we are thankful to all volunteers who participated in the experiments. The research was supported by Deutsche Forschungsgemeinschaft (grant HE 2122/6-1).

Notes

1. The minimum safety margin is defined as the interval between the last perceived moment of safety to initiate an action and the perceived (anticipated) moment of collision.

2. In the following, this variable will be termed ‘mirror distance’, defining the distance between the observer's eye to the centre of the mirror.

3. In the following, this variable will be termed ‘simulation size’, meaning the absolute size of the simulation.

4. Eighty per cent of the participants in the moderate radius group reported that their car is equipped with at least one convex mirror.