Analysis of Stopping Sight Distance (SSD) Parameters: A Review Study

Abstract

Stopping sight distance (SSD) is one of the important elements in geometric highway design, which relies on the two key parameters, i.e., vehicle braking characteristics and drivers' reaction time. Previous studies have shown higher discrepancies in the coefficients of the SSD parameters, and therefore, making it difficult for practitioners what values to be followed. Therefore, this review study aims to compare deceleration rates and PRT values in different situations that can be applied to geometric highway design. To this end, two electronic databases were searched and relevant articles that reported drivers' perception reaction time (PRT) or deceleration rates in different situations were identified and included in the review. The obtained results showed that deceleration rates of vehicles ranged from 0.49 m/s2to 8.76 m/s2with a total weighted average of 2.82 m/s2. On the other hand, PRT of drivers ranged from 0.48 seconds to 2.01 seconds, with a total weighted average of 1.21 seconds. The key factors that were assessed on deceleration rate of vehicles are surface condition; vehicle type; stimulus; and initial speed. Results of this study suggest that all these factors, except for initial speeds greater than 80 km/h, have a significant effect on deceleration rates of vehicles. The findings of this study could be used as inputs in geometric highway design calculations under different conditions.