CAPACITY DROP AT T-JUNCTIONS: MODELING AND SIMULATION OF BASSAWA–PALLADAN JUNCTION, ZARIA

Abstract

This study investigates the capacity drop phenomenon at T-junctions using a modelling and simulation approach. Capacity drop, defined as the reduction in queue discharge flow compared to pre-queue capacity, is a recurrent yet under-researched challenge in traffic engineering. Using traffic flow data collected at the Bassawa-Palladan T-junction in Zaria, the study applies Poisson processes and Markov chains to develop a stochastic model. The model simulates the interaction of mainstream and junction outflow traffic, with time delays used as key indicators. MATLAB simulations with both randomly generated data and real field observations reveal that capacity drop probability increases exponentially with time vehicles are halted at the mainstream. A critical threshold of 45 seconds in the morning and 65 seconds in the evening was identified, beyond which the probability of capacity drops trends toward certainty (approximately 1). The study recommends integrating these empirical thresholds in traffic control designs for the junction and other junctions to minimize delays and improve flow efficiency.