Countering distractions to visual detection when driving after dark

On main roads, such as motorways and dual carriageways, road lighting is designed to meet the needs of drivers. Well-designed road lighting is intended to support visual performance and visual comfort after dark, and therefore this has been the dominant concentration of previous research. Less attention has been paid to the extent to which lighting can support driver attentiveness, a critical factor for driving since failure to give sufficient attention is a causal factor in many road traffic collisions. Therefore, this thesis reports further investigation of the extent to which light can be used to mitigate drivers’ inattention. Two laboratory experiments were conducted to investigate how light can be utilized to counter driver inattention due to sleepiness or distraction.
Experiment 1 investigated the effect of lighting on sleepiness mitigation conducted after dark and three hours before habitual bedtime to simulate driving in the evening. This experiment assessed sleepiness under four lighting conditions with melanopic EDIs ranging from less than half lux to 10 lx. The results did not suggest a significant effect of lighting on sleepiness as measured by salivatory melatonin level, audio reaction time, skin temperature and self-reported sleepiness.
Experiment 2 investigated the visual and non-visual benefits of light in mitigating drivers’ distraction using a scale model of a road scene containing three potential hazards: a road surface obstacle, vehicle lane change and a pedestrian. Participants' reaction time to and probability of detection were investigated in the presence of visual or acoustic distraction. The assumption in this experiment was that distraction negatively affects hazard detection, which can be mitigated by higher road surface luminance, in-vehicle short-wavelength blue light, and pedestrian-worn “aids to vision”. The results indicate visual distraction impairs hazard detection while acoustic distraction does not. An increment in road surface luminance improved hazard detection but was not enough to overcome the negative impact of visual distraction. In-vehicle short-wavelength blue light improved cognitive performance of distraction tasks but did not transfer into hazard detection. Finally, a flashing LED light has been found to be superior to road lighting in mitigating visual distraction for pedestrian detection.
The findings from these experiments do not suggest that road lighting can be used to effectively mitigate driver sleepiness after dark. While concerns persist about the potential negative effects of road lighting on sleep health, the experimental result of this work did not find melatonin suppression even under the highest light level of current road lighting standards, suggesting no impact on drivers’ sleep health. Furthermore, the results did not suggest that in-vehicle short-wavelength blue light mitigates the negative impact of distraction but may also exacerbate visual performance and hazard detection challenges. Future research should investigate potential ocular alterations and pupillary changes which might be induced by the installation of an in-vehicle light system.