The impact of road lighting on road user alertness in the evening

Alshdaifat, A.; Moadab, NH; Fotios, Steve · 2023 · OpenAlex-citations

DOI: 10.1177/14771535231172687

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Summary

This study investigates whether road lighting conditions significantly affect road user alertness in the evening, addressing a gap in current lighting guidance which focuses primarily on visual performance rather than non-visual physiological effects. The research was motivated by the potential for lighting to stimulate intrinsically photosensitive retinal ganglion cells (ipRGCs) and thereby improve alertness, a factor linked to reduced risk of road traffic collisions. Specifically, the study aimed to verify previous findings from a test track study that found no significant impact of lighting on alertness, while testing a higher melanopic equivalent daylight illuminance (EDI) to ensure sufficient ipRGC stimulation. The researchers conducted a laboratory experiment with 40 participants aged 18–30. After a two-hour adaptation period under lighting simulating a domestic interior (25 lx photopic, 10.7 lx melanopic EDI), participants were exposed for one hour to one of four test lighting conditions. These conditions varied in illuminance and spectral power distribution, resulting in melanopic EDI levels ranging from <0.5 lx to approximately 10.4 lx. Half of the participants remained seated to simulate driving, while the other half walked on a treadmill to simulate pedestrian activity. Alertness was measured using four dependent variables: salivary melatonin levels, reaction time to an acoustic psychomotor vigilance test, self-reported sleepiness via the Karolinska Sleepiness Scale (KSS), and skin temperature. The results indicated that differences between the four lighting conditions did not have a statistically significant effect on any of the dependent variables. While melatonin levels increased significantly over time as participants approached their habitual bedtime, this trend was consistent across all lighting groups. Similarly, self-reported sleepiness increased over time, and reaction times slowed initially before stabilizing, but none of these changes were influenced by the specific lighting condition or the participant's posture (seated vs. walking). There were no significant interactions between lighting condition, posture, or test intervals for any of the measured outcomes. The study concludes that the alerting effect of road lighting is not significant for driving or walking in the evening, even when melanopic EDI is increased to levels up to 10 lx. These findings confirm earlier results from a test track study and suggest that current road lighting practices, which do not prioritize non-visual effects, are sufficient regarding alertness. The lack of significant impact implies that enhancing the spectral content or intensity of road lighting within typical ranges does not provide a measurable benefit for maintaining road user alertness during evening hours.

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Topics

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• roadway lighting effects
• circadian factors
• dark adaptation mesopic
• visibility analysis litigation