Impact Assessment of Tricycle’s Proportion on Saturation Flow Rate at Urban Signalized Intersections

Abstract

Tricycles constitute a substantial proportion of traffic in Kano and other cities in Nigeria. This study assesses the impact tricycle’s proportion on saturation flow rate at six selected signalized intersections in Kano metropolis. Two methods; Highway Capacity Manual (HCM) model and empirical approaches were used to evaluate saturation flow rates at the selected intersections and results compared. Saturation flow rate was estimated using the HCM model approach based on intersection’s geometric features and vehicle’s adjustment factors, excluding tricycles. In the empirical approach, saturation flow rate per intersection’s approach was estimated based on the number of vehicles (tricycles inclusive) that crossed the stop-line per effective green-time of an approach. Results obtained from the study showed that saturation flow rates from empirical approach ranges from 2,885 to 8,626 veh/hr, while that from the HCM model approach, it ranges from 3,906 to 10,891 veh/hr. On the average scale, saturation flow rates of 5,964 veh/hr and 7,446 veh/hr were recorded for the empirical and HCM model approaches, respectively. On the overall scale; 20 out of the 21 approaches of the 6 studied intersections recorded higher saturation flow rates based on the HCM model relative to those estimated based on the empirical method. A test of significance using independent t-test was performed at 95% confidence level to ascertain whether there is statistically significant difference between saturation flow rates values obtained from empirical and HCM model approaches. Results from this test revealed a P-value 0.04 (P < 0.05), which indicates that there is statistically significant difference between the results obtained from the two approaches. This implies that the HCM model overestimated the saturation flow rate relative to the empirical approach. The implication of this finding is that saturation flow rates based HCM model would lead to erroneous designation of an intersection’s operational performance or level of service; specifically, denoting a premature operational failure of the facility. This would consequently suggest for a premature facility improvement with associated unjustified expenditures.