Research on the influence of rainfall characteristics on driver visual distance under low-light conditions at night

Abstract Nighttime driving primarily depends on low-beam headlight illumination for obstacle recognition. During rainfall, extinction by raindrops causes significant light attenuation and scattering, which degrades critical visual information and consequently reduces drivers’ recognition ability and increases safety risks. This study investigates the mechanisms that degrade drivers’ visual recognition under low-light nighttime rainfall and quantifies the effects of different rainfall characteristics on drivers’ visual distance. Static and dynamic experiments were conducted with 24 licensed drivers, using standard low-beam headlights and small gray targets, over rainfall intensities (I) of 0.2−11.6 mm/h and median volume diameters (D50) of 0.31−2.75 mm. The results indicate that D50 is a more sensitive indicator than rainfall intensity (I) for quantifying reductions in visual distance. Both static visual distance and its attenuation rate exhibit a pronounced quadratic relationship with D50, with minimum attenuation at D50 = 0.96 mm and pronounced reductions at the lower and upper extremes. A quadratic regression model for static visual distance was established, and dynamic experiments yielded speed-dependent correction factors, resulting in a predictive model that integrates raindrop microphysics and vehicle speed. The findings provide a quantitative basis for dynamic speed limits, hazard-warning thresholds, and visibility-based traffic management under nighttime rainfall, and may improve crash prevention strategies in low-light and adverse-weather environments.