Empirical and Simulation Based Safety Evaluation of Forced Gap Behaviour at an Urban Unsignalised Intersection under Mixed Traffic

Abstract

Unsignalised intersections present significant safety risks due to uncontrolled conflicts between vehicles on major and minor roads, especially during right-turn manoeuvres. This study examines the impact of speed bumps in reducing forced gap behaviour at anunsignalised intersection using a variety of surrogate safety indicators. Forced gap behaviour occurs when vehicles on a major road reduce their speed in response to aggressive right-turn manoeuvres from minor roads. Data was collected using a videographic technique at a Tintersection in the Thiruvananthapuram district of Kerala, India. The study analyses changes in the forced gap behaviour of vehicles at unsignalised intersections using various surrogate safety indicators, including Post Encroachment Time (PET), Occupancy Time at the conflict area (OT) and Speed Differential Percentage (SDP). The study found that when no speed bump was present, PET values ranging from 0 to -5 seconds accounted for 36.57% of the total sample size. However, this percentage increased to 55.72% when a speed bump was implemented indicating a reduced forced gap behaviour. A VISSIM simulation-based analysis indicated that the presence of higher proportion of motorised two-wheelers increases the forced gap behaviour (PET ∈ [-5, 0]) even under the presence of a speed bump.