Accident Analysis and Prevention 63 (2014) 83–88 Contents lists available at ScienceDirect Accident Analysis and Prevention journal h om epage: www.elsevier.com/locate/aap Measuring the effect of the rainfall on the windshield in terms of visual performance Frédéric Bernardin a , Roland Bremond b,∗ , Vincent Ledoux a , Maria Pinto b , Sophie Lemonnier b , Viola Cavallo b , Michèle Colomb a a Centre d’Études et d’Expertise sur les Risques, l’Environnement, la Mobilité et l’Aménagement (CEREMA), Bron, France b Institut Franc ¸ ais des Sciences et Technologies des Transports, de l’Aménagement et des réseaux (IFSTTAR), LEPSIS Lab, Champs-sur-Marne, France a r t i c l e i n f o Article history: Received 26 April 2013 Received in revised form 23 September 2013 Accepted 10 October 2013 Keywords: Visual performance Driving Rain Methodology a b s t r a c t Driving through rain results in reduced visual performance, and car designers have proposed counter- measures in order to reduce the impact of rain on driving performance. In this paper, we propose a methodology dedicated to the quantitative estimation of the loss of visual performance due to the falling rain. We have considered the rain falling on the windshield as the main factor which reduces visual performance in driving. A laboratory experiment was conducted with 40 participants. The reduction of visual performance through rain was considered with respect to two driving tasks: the detection of an object on the road (contrast threshold) and reading a road sign. This experiment was conducted in a laboratory under controlled artificial rain. Two levels of rain intensity were compared, as well as two wiper conditions (new and worn), while the reference condition was without rain. The reference driving situation was night driving. Effects of both the rain level and the wipers characteristics were found, which validates the proposed methodology for the quantitative estimation of rain countermeasures in terms of visual performance. © 2013 Elsevier Ltd. All rights reserved. 1. Road safety under rain Rain may affect driving performance, and since the beginning of automotive transport, car designers have considered this issue. They have proposed countermeasures in order to reduce the impact of rain as early as 1903, when Mary Anderson proposed the first patent for a windshield wiper (Anderson, 1903). In addition to wipers, rain effects are also mitigated by improved windshield design, automotive lighting and road lighting. Considering the high impact of rain on vision, and even though the main impact of rain on driving addresses the road skid resistance, one may be sur- prised that the quantitative impact of rain on the driver’s visual performance led to very few studies to date. In his accidentology review, Parkarri (2009) found that low vis- ibility conditions, such as rain, fog and night driving, increase the risk of having an accident. More specifically, in rainy conditions, accidents with three and more vehicles are more frequent. The risk increases due to rain also depend on road conditions (higher on motorways, in curves and slopes) and on the road user (higher for cars and pedestrians). He also found that the risk increase is higher under strong rain compared to light rain. ∗ Corresponding author. Tel.: +33 1 8166 8534. E-mail address: roland.bremond@ifsttar.fr (R. Bremond). Based on a comparison of accident data with and without rain, Andrey and Yagar (1993) found that the crash risk was 70% higher under falling rain compared to without rain. Interestingly, they found that this higher risk does not appear after rain, driving on a wet road. They proposed an explanation in terms of risk compen- sation (Wilde, 1988), arguing that drivers compensate for the skid resistance risk associated to a wet road, but not for the lowered visi- bility due to the falling rain. These results were confirmed by Chung et al. (2005) on the Tokyo Metropolitan Expressway, with an acci- dent rate of 1.5/h under rain vs. 0.8 without rain. Another study in Melbourne (Australia) found that rain, rain intensity and night situation all three result in higher risk levels (Keay and Simmonds, 2005). These results about accident rates are however mitigated by the accident severity data. From 10 years of accident studies in the UK, Edwards (1998) found that the severity of accidents under rain is less important compared to without rain, which may be due to the lower speed (Khatak et al., 1998). In addition to the higher risk due to a lower skid resistance, these results from accident studies could be expected from the visual effects of rain on visual performance. Three main effects can be anticipated: first, wet surfaces differ in their visual appearance from dry surfaces; second, the rain lowers the contrast between the objects and their background, thus lowering the driver’s detection performance; third and most important, the raindrops on the wind- shield alter the visibility, in a way which is not well understood. 0001-4575/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.aap.2013.10.008