Effects of Motorcycles on Saturation Flow Rates of Mixed Traffic at Signalized Intersections in Ghana

Saturation flows which are important for the design of signalized intersections and capacity analysis depend on the vehicle mix in the traffic stream. Traffic mix in the Savannah Accelerated Development Authority (SADA) zone in Ghana may be classified as mixed due to the high proportion of motorcycles; this makes it very different from the rest of Ghana. In this study, passenger car unit values and saturation flow rates were determined at three signalized intersections in the Tamale metropolis. Traffic volume at the three signal intersection approaches were videotaped during the peak to ensure saturation flow and queuing conditions. The three hour films were played on a laptop computer and the traffic flow manually classified into four groups: motorcycles, tricycles, car/taxis and buses/trucks. The data were analyzed using regression techniques to determine saturation flow. Average saturation flow values of between 3252 pcu/hr and 3810 pcu/hr were observed with the high values being as a result of the high proportion of motorcycles in the traffic. The results show that the higher the motorcycles on any approach the lower the headway and the higher the saturation flow.