CAPACITY AND LEVEL-OF-SERVICE ASSESSMENT OF RUMUOKORO ROUNDABOUT IN THE CITY OF PORT HARCOURT UNDER MIXED TRAFFIC

Abstract

Rapid motorisation and uncoordinated land-use growth along arterial corridors in Port Harcourt, Nigeria, have overloaded many at-grade junctions, including roundabouts originally designed for far lower demand. This study evaluated the operational performance of the five-leg Rumuokoro Roundabout, a key node linking the Choba, Eliozu, Rumuokwota, Rumuaholu and Rumuodomaya corridors. Geometric data (inscribed circle diameter, entry width, entry radius, entry angle, flare length and weaving length) were obtained with a laser distance measurer, while classified traffic volumes, U-turn proportions, heavy-vehicle percentages, gap acceptance, queue lengths and pedestrian crossing demand were recorded using video recording, tally sheets and a digital stopwatch during weekday morning and evening peak periods. Entry speeds were measured with a laser speed gun to obtain the 85th-percentile value. Entry capacity at each leg was estimated using the Kimber empirical regression model, and level of service (LOS) was assigned using Highway Capacity Manual control-delay thresholds adapted for roundabouts. Results showed a substandard inscribed circle diameter (42.3 m), zero flare length, a short weaving length (22–28 m) and an 85th-percentile entry speed of 48 km/h, all outside recommended limits. Volume-to-capacity ratios ranged from 1.31 to 1.79 across the five legs, with control delays between 201 and 312 seconds per vehicle, placing every approach in LOS F (breakdown condition). The Choba and Eliozu approaches, carrying the highest through volumes and heavy-vehicle shares, recorded the longest queues (up to 625 m) and highest delays. The findings indicate that geometric deficiencies rather than volume alone are driving the roundabout's failure, and the paper recommends geometric retrofitting, entry-speed control and a review of the intersection control strategy.