The effect of different road lighting levels on drivers’ visual performance under various conditions

Traffic accidents are one of the leading causes of death globally. Accident rates are higher during darkness than during daylight. Some of the potential contributing factors in accidents are low visibility and impaired driving due to e.g. alcohol, drugs, distraction or fatigue. Introducing road lighting can mitigate the amount and severity of accidents that are due to low visual performance. However, at the same time, energy consumption and related costs of road lighting are the driving forces for more efficient road lighting technologies. Therefore, the transition of the road lighting to intelligent road lighting system that could tackle energy, cost, and safety challenges is inevitable. So far, not much research can been found about the combined effect of different road light intensities and car headlights on drivers' visual performance. The aim of this dissertation is to provide such information under realistic conditions. The results can be used in the development of intelligent road lighting practices. Several measures were executed in a stationary car with a constant distance to the targets. Drivers' visual performance was investigated under various road surface conditions (dry, wet and snowy), different road lighting levels, and presence or absence of glare. Finally, detection distance study was designed to determine whether similar results can be found in a moving car. Various methods were applied to study driver's visual performance such as contrast, Visibility Level, psycho-visual tests, and detection distance. All measures suggested similar conclusions. The results of this study indicated that the current practice of road lighting levels for motorised traffic is not always necessary. In the presence of car headlights, with no glare from oncoming cars, headlights alone, or combined with a low lighting level, provided better visibility performance than when combined with full lighting intensity. In addition, the effect of different road lighting levels was not monotonic, because reducing road lighting shifted the contrast from positive to negative polarity or vice versa and made the contrast approach zero in some conditions. Therefore, road lighting should be lowered to a level that does not neutralize the effect of car headlights. This result supports the feasibility of reducing road lighting level under different road surface conditions. In the presence of glare from an oncoming car, higher road lighting level provided better visibility than lower lighting levels, but the effect of different road lighting intensities on visual performance was not statistically significant.