Empirical evaluation of vehicle safety envelope across vehicle type and speed in disordered traffic condition

Real-time safety assessments face unique challenges in developing economies due to the disordered and high heterogeneity in traffic. This study proposes a dynamic two-dimensional surrogate safety model, known as the Vehicle Safety Envelope (VSE), that represents the minimum space required around a vehicle for safe and comfortable manoeuvring in traffic. The VSE is mathematically modelled and calibrated using trajectory data collected from five signalized intersections in India. The proposed elliptical shape of the VSE was found to be analogous to the field observed safety space maintained by a vehicle from its neighbouring vehicles for safe and comfortable manoeuvres. Empirical results indicate that both lateral and longitudinal clearance thresholds, the key parameters defining the VSE, exhibit a positive linear dependency on vehicle type and speed. As speed increased from 5 to 65 km/h, the lateral clearance threshold increased from 0.2 m to 0.8 m for two-wheelers and from 0.6 m to 1.2 m for heavy commercial vehicles. Similarly, the average longitudinal clearance threshold increased from 1 m to 14 m. These thresholds closely matched safe stopping distances calculated from field data, validating the VSE's capability to capture unsafe vehicle proximities. Integrating VSE into advanced driver-assistance systems could enhance proactive safety decision-making.