Lateral distance-keeping behaviour of drivers in foggy weather

Fog contributes to nearly 21% of global road accidents, with mixed traffic and weak lane discipline amplifying risks. Unlike prior studies focusing mainly on longitudinal visibility, this work highlights the overlooked role of lateral manoeuvring in fog. Using trajectory data from naturalistic traffic videos, lateral gaps and speeds were extracted across three visibility regimes: dense fog (0–200 m), medium/shallow fog (200–800 m), and clear conditions. Results show that the average lateral gap is significantly reduced in dense fog (140.6 cm at 50 km/h) compared with clear weather (168.4 cm), with gap-speed relationships steepest in dense fog but negligible in medium fog. Vehicle heterogeneity strongly shapes risk: cars maintain dangerously narrow gaps with other cars, and two-wheelers fail to increase gaps with speed, while heavy commercial vehicles adopt safer spacing. The novelty of this study lies in quantifying lateral interaction dynamics under fog, refining mixed-traffic simulation models, and offering evidence-based insights for traffic management. Practical implications include enforcing lane discipline, restricting overtaking in fog-prone stretches, and segregating risky vehicle pairs to reduce side-swipe collisions. These findings provide both a scientific contribution and actionable guidance, advancing fog-specific safety management and intelligent system design.