Collaborative effects of vehicle speed and illumination gradient at highway intersection exits on drivers’ stress response capacity

Inadequate visibility is a critical factor contributing to the heightened occurrence of nighttime accidents at highway intersections. The installation of smart streetlights which are equipped to detect vehicle positions and speed information, thereby dynamically adjusting illumination, offers a promising solution to significantly reduce nighttime accident rates while conserving lighting energy. Nevertheless, as vehicles travel through illuminated intersections in a relative high speed and enter unlighted highway segments, drivers often experience dynamic visual illusions during dark adaptation, consequently impairing their stress response capacity and generating driving safety concerns. Therefore, we investigate the collaborative impact of illumination gradient and vehicle speed at intersection exits on driver stress response, aiming to provide a theoretical foundation for gradual illumination designs dynamically aligning with various vehicle speeds. Specifically, with reaction time employed as a metric to quantify driver stress response, and intersection area illuminance and vehicle speed utilized as input parameters, a safety assessment method for illumination gradients at exit sections is developed using variance analysis and multiple comparison techniques. Subsequently, a high-fidelity nighttime driving simulation platform is established, integrating initial illuminance, vehicle speed, and illumination gradient distance within exit sections as influential factors. Through simulated driving experiments, the collaborative effects of illumination gradient schemes and vehicle speed on reaction time is systematically examined. Ultimately, we propose optimal illumination gradient schemes and the minimum required number of streetlights for exit sections corresponding to specific vehicle speeds. Results reveal that exit section illumination is unnecessary when the vehicle speed is below 40 km·h⁻¹. For vehicle speeds of 50, 60, and 70 km·h⁻¹, the minimum required exit section lengths are determined to be 35, 70, and 105 m, respectively. Moreover, it is established that a minimum of one streetlight is indispensable within the exit section at a speed limit of 50 km·h⁻¹, while at 60 km·h⁻¹, at least two streetlights are required. Lastly, under a speed limit of 70 km·h⁻¹, the exit section should accommodate no fewer than three streetlights to ensure optimal safety conditions.