DESIGN OF A TRAFFIC SIGNALISATION SCHEME AT OLA-OLU INTERSECTION, ILORIN, NIGERIA

Adeleke, Oluwafemi Oyetunde; Adeogun, Kabiru Abiodun; Kolo, Stephen Sunday · 2020 · Crossref

DOI: 10.11113/mjce.v32n2.639

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Summary

This study addresses the traffic congestion and safety hazards at the Ola-Olu T-intersection in Ilorin, Nigeria, a developing urban center lacking efficient mass transit. The intersection, currently managed by manual traffic wardens during peak hours, suffers from high delays and weekly traffic crashes. The research aims to ameliorate these issues by designing a fixed-time traffic signalization scheme. The specific objectives were to determine the intersection’s geometric layout, analyze traffic volume and vehicular turning movements, and design appropriate signal timings. The methodology involved field surveys and data collection conducted in May 2019. Geometric parameters, including approach widths and slopes, were measured using Total Station instruments. A 12-hour, 15-minute interval classified traffic count was performed manually over seven days from 7 am to 7 pm, with three observers per approach. Data were converted to Passenger Car Units (PCU) using Nigerian standards. The study confirmed that signal installation was warranted based on vehicular volume, crash experience, and road network criteria. Saturation flow rates were calculated using the Highway Capacity Manual model, incorporating adjustment factors for lane width, heavy vehicles, grade, and turning movements. The results established a 3-phase fixed-time signal plan with an optimum cycle length of 155 seconds, derived using Webster’s method. Phase 1, allocated 102 seconds of green time, handles non-conflicting through movements from the A-Division and Gaa-Akanbi approaches. Phase 2, with 16 seconds of green time, accommodates left turns from Gaa-Akanbi and U-turns from A-Division. Phase 3, assigned 22 seconds, manages left turns from the Gaa-Imam approach. Each phase includes a 3-second amber time and a 2-second all-red clearance time. Analysis of the critical flow ratios (summing to 0.821) and actual lane group capacities confirmed that the proposed design is adequate and that the intersection geometry does not require additional lanes. The significance of this work lies in providing a data-driven solution to replace inefficient manual traffic control. The authors conclude that implementing this signalization scheme will enhance traffic flow, reduce conflicts, and lower the frequency of crashes at the intersection. Additionally, it eliminates the need for traffic wardens at this location. The study recommends further research on other critical intersections in Ilorin and the implementation of pavement markings to improve lane discipline, as such markings are currently absent. This research contributes to the field of traffic engineering in developing economies by demonstrating the application of standard signal design methods to local conditions.

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• intersection design