Judging the approach speed of motorcycles and cars under different lighting conditions Mark Gould 1 , John Wann 1 , Damian Poulter 1 , Shaun Helman 2 1 Royal Holloway, University of London, UK 2 Transport Research Laboratory, UK Methodology • 14 participants aged from 22 to 49 years of age (Mean 32 years). • Adaptive (BEST-PEST) staircase procedure. • All main headlight diameters set to 20cm. Tri-headlight flanking lights set to a diameter of 10cm. • Reference car stimulus that travelled at 30 mph. • Sequential stimulus presentation • Task - “which vehicle was travelling fastest?” • Vehicle images / headlights changed in size and expansion to simulate approach. • A TTP of 4 seconds was used across all experiments. • Speed judgments made across five different lighting conditions. • Photo-realistic images of a car and motorcycle were presented in a virtual city environment • The environment and stimuli were both reactive to the overall ambient light level. Discussion • Speed judgments for cars constant across all lighting levels • Speed judgments for solo headlight motorcycles significantly impaired under low level lighting conditions • Inclusion of tri-headlight formation significantly improves accuracy under low light level conditions • Can the tri-headlight formation improve conspicuity? • Important to inform drivers that even once a motorcycle is detected within a scene, speed judgments may still be inaccurate • Important to stress that speed misperception is likely to increase under low luminance Funded by the United Kingdom Engineering and Physical Sciences Research Council (Grant EP/P504309/1). Results • Two way repeated measures ANOVA revealed a significant main effect of light level (p < .01) and a significant main effect of vehicle type (p < .001). • The ANOVA also revealed a significant interaction between light level and vehicle type (p < .01). Introduction • Disproportionate number of traffic accidents occur after dark (Plainis et al. 2006). • 50% of fatal accidents occur between the hours of 6am and 6pm (CARE, 2007). • Driver vision in the dark is seriously impaired compared with daylight (Sullivan et al. 2004). • Drivers can gauge the speed of a vehicle by dividing the optical size by the rate of expansion (Lee, 1976). • Larger vehicles will loom to a greater extent than smaller vehicles (Horswill et al. 2005). • Drivers are poor at judging the speed of motorcycles at night due to insufficient surface area provided by the solo motorcycle headlight (Gould et al. In Press). • Motion perception using rod photoreceptors is significantly impaired (Gegenfurtner et al. 1999). • Higher than average number of ROWV involving a motorcyclist occur during low lighting conditions (Pai et al. 2009). Vehicles • Driver performance for judging the speed of the car stimulus did not significantly differ across lighting conditions • Driver performance for judging the speed of the solo headlight motorcycle was significantly more accurate in the daylight condition compared with the early night (p < .05) and the nighttime (p < .01) conditions. Driver performance for judging the speed of the solo headlight motorcycle was also significantly more accurate in the lower daylight condition compared with the nighttime condition (p < .05) and in the dusk condition compared with the nighttime condition (p < .05) • Driver performance for judging the speed of the tri-headlight motorcycle stimulus did not significantly differ across lighting conditions Lighting Levels • Participants were more accurate at judging the speed of the car compared with the solo headlight motorcycle across all conditions (p < .05). • Participants were more accurate at judging the speed of the car compared with the tri- headlight motorcycle in the lower daylight and nighttime conditions (p < .05). • Participants were more accurate at judging the speed of the tri-headlight motorcycle compared with the solo headlight motorcycle in the early night and nighttime conditions (p < .05). Day Lower Daylight Dusk Early Night Night 0 10 20 30 40 50 60 70 80 90 Solo Motorcycle Car Light Level Speed Difference (mph) Fig. 1b Lower Daylight Condition Fig. 1a Daylight Condition Fig. 1c Dusk Condition Fig. 1d Early Night Condition Fig. 1e Nighttime Condition