ESTIMATION OF SATURATION FLOW AT SIGNAL CONTROLLED INTERSECTIONS

Abstract

The general term intersection describes all roadway situations where two or more roads join or cross one another at the same or different elevation. In developing countries like India crossing of two roads at same level is a common feature because later is very expensive. Design of an at-grade intersection under mixed traffic flow conditions to handle the crossing traffic at satisfactory level of services is the biggest problem encountered by traffic engineers. It is generally observed that congestion at intersection occurs at volume level well below the capacity. Saturation flow and green time ratio are the two factors on which the capacity of the signal controlled intersection depends. Saturation flow will be affected by the several geometric, operating, traffic, environmental and other kind of parameters. For the design of efficient and safe intersection to serve the needs of the existing and future coming traffic it is necessary to have an idea on all kind of affecting parameters of saturation flow. In this Dissertation topic attempt has been made to study the concept of saturation flow at signal control intersections and the influence of approach width, traffic composition and turning movement on saturation flow. Data collected at 12 signal controlled intersections, were analysed to estimate the saturation flows for different approaches and to investigate the effect of approach width, turning movement and heavy vehicles proportion on the saturation flow. The vehicles are categorized in to five categories. It is observed that Saturation flow increases with the increase in the proportion of 2-wheelers. Relationships have been established between proportions of vehicle categories and saturation flow. Influence of proportion of heavy vehicles on saturation flow for through movements is examined and presented graphically. Saturation flow of an approach decreases with the proportion of heavy vehicles in the traffic flow which is discharging from that approach. Two more relations have been developed between saturation flow rate and approach width and in between saturation flow rate and RT proportion. It has been observed that with increase in approach width and with decrease in RT proportion, SF increases.