Gradient illumination scheme design at the highway intersection entrance considering driver's light adaption

Improving lighting arrangements at the highway intersections can significantly reduce the likelihood of crashes. Meanwhile, a reasonable gradient illumination scheme can increase drivers' safety by avoiding the rapid change of their pupil area when driving from an unlighted area into a lighted area. The purpose of this study is to design illumination transition zones for drivers when approaching the highway intersection, and optimize the illumination increments along the transition zones.

This issue is addressed in three stages. First, an indoor simulation platform is built using the UC-win/road software, and its parameters are calibrated using real intersection data collected at night. Second, the variation of pupil area under different increasing rates of illuminance near the driver's eyes (INDE) is analyzed, and a model representing the temporal change of the area in the pupil contraction stage is established. Last, an optimization model is proposed to obtain the optimal luminance increasing rates by minimizing the time needed for drivers to travel through the transition zones under different maximum illuminations and speed limits.

The findings of this study indicate that the INDE increasing time in the transition zone remains unchanged with a determined illumination at the intersection, and the optimal transition zone length is directly proportional to the speed limit of the intersection. Therefore, the transition zone length needs to be adjusted to accommodate different speed limits: it should be extended or shortened by the same percentage as the increase or decrease of the speed limit.

It can be concluded that the illumination transition zone is necessary when the INDE of highway intersection and the speed limit exceed 8 lx and 40 km/h, respectively. The INDE increasing rate should be maintained around the optimal value, providing safe and comfortable light adaptation to drivers and preventing traffic accidents. The study will provide a scientific basis for safety implementation of lighting arrangements at highway intersections.