EFFECT OF MIXED TRAFFIC ON SATURATION FLOW

Abstract

The road traffic in the developing countries like India is more likely to be mixed or heterogeneous in nature. Different types of vehicles, varying both in static and dynamic characteristics, ply on the roads. Signal controlled intersection is one of the basic form of traffic control measure which is used in both, developed and developing nations, to ensure safety and movement efficiency in the intersection area. Geometric parameters, operating conditions, traffic compositions and various other factors affect the saturation flow at the signal controlled intersections. The conditions in developed nations are quite different from those at the similar intersections of developing nations. This study has been taken up to study and analyze the effect of varying composition of traffic flow on the saturation flow that discharges from an approach. Saturation flow and green time ratio are the common factors on which the basic capacity of signalized intersections depends. Both factors are affected by geometric characteristics and traffic behavior, operating conditions, environmental and other prevailing conditions. In order to design a safe and efficient intersection, so that the needs of the existing and future traffic can be met, it is necessary to have an idea of all kinds of affecting parameters for saturation flow. Traffic data is collected during peak hours on two intersections namely Airport chowk and Press chowk in Chandigarh city, India and same is brought back to office to extract desired information using ‘K-Lite Codec’ software. The data so analyzed includes traffic volume during saturation period, traffic composition in different cycles, equivalent hourly volume and estimation of saturation flow in pcu/hr/m width of lane at both the intersections. The graphs were plotted for variation of vehicle share and effective green time against saturation flow and an attempt was made to develop model between saturation flow and percent share of different vehicles at both the intersections. Analyses at Airport Chowk shows that there are sufficient cars, buses and tempo on all lanes and at Press Chowk 2W and 3W occupies sufficient space on middle and shoulder lane, whereas, Cars occupies median and middle lane and there is negligible percentage of heavy vehicles in all the approaches. On analysing saturation flow with respect to effective green time at Airport Chowk it was noted that there is no regular pattern of increase or decrease in saturation flow. This indicates the effect of mixed traffic on saturation flow, whereas in homogeneous traffic, saturation flow generally increases with increase in effective green time. But at Press Chowk, peak values or repeated value of saturation flow can be iv noted in for effective green time between 35-55 seconds. R2 value for models developed are 0.999, 0.997 and 0.933 which explains the least variation in data points with respect to the estimated model.