An Evaluation of the Spatiotemporal Variation in the Degree of Saturation of Traffic at Signalised Roundabouts in a Typical Nigerian City

Abstract

The degrees of saturation of traffic at the approaches to the two major signalised junctions, Fajuyi Roundabout, and Matthew Roundabout at Ado Ekiti, Nigeria, which are spaced at approximately 500m, were determined for the weekdays and weekend. In general, the results showed morning peaks at 7am-9am, evening peaks at 3pm-6pm and inter-peaks between these periods, especially around noon during weekdays at the roundabouts. There were mainly low-value peaks at 7am-9am and 3pm-5pm respectively on Saturday while the values on Sunday were mainly uniform; and the lowest. The most significant differences in the traffic flow at the two junctions were the congestion being experienced at Irona Street approach of Matthew Roundabout during weekdays, and the high degree of saturation of traffic between 12noon-5pm at the Ijigbo Street approach of the roundabout on Sunday. Even with this, there was relative similarity in the temporal variation of the degree of saturation of traffic at the two roundabouts, which was attributed to the similarity in their location, and thus traffic flow, as both are sited at the city centre. Other contributory factors include the short spacing and comparable land-use.

Keywords: degree of saturation, signalised roundabout, traffic control lights, congestion, traffic stream