A positive-contrast approach to improve cyclist visibility in road lighting

Cyclist visibility in road lighting environments is a key factor in reducing crash risks, particularly in conflict zones where interactions with motorised traffic occur. Existing lighting standards predominantly focus on horizontal illuminance, which does not sufficiently address the visibility challenges cyclists face in these high-risk areas. This study introduces a novel positive-contrast model that incorporates vertical illuminance as a supplemental parameter, specifically for conflict zones. The theoretical model assesses the impact of vertical illuminance on visibility levels, demonstrating that a minimum threshold is necessary to achieve positive contrast and prevent veiling effects that reduce conspicuity. A computational optimisation process was employed to identify feasible lighting configurations, and the model was validated through a simulation-based evaluation of light distribution curves. The findings indicate that optimised lighting designs can meet the proposed vertical illuminance requirements without excessive glare or energy consumption. Consequently, the study highlights the need for tailored luminaires to facilitate real-world validation and implementation of this approach. Further field studies are essential to verify these findings and establish practical design recommendations for urban lighting planners.