EFFECT OF RIGHT TURNING VEHICLES ON SATURATION FLOW THROUGH SIGNALISED INTERSECTION

Abstract

The capacity analysis procedure for a signalised intersection is based on the concept of saturation flow and saturation flow rates which is the maximum rate at which traffic can pass with 100 percent of real time available as effective green time. Presence of right turning vehicles affects the saturation flow of a signalised intersection by infulencing the flow of through moving vehicles. When the right turn movement is independent of the straight through movement then saturation flow of the intersection is affected by allocation of cycle time for the right turners and provision of separate lanes for such vehicles. When the right turn is combined with the straight movement then the turning vehicles interfere with through moving vehicles. In the present study it is attempted to compare the saturation flow of right turning vehicles with that of straight moving vehicles at few selected signalised intersection of New Delhi and to develop PCU curves for right turning vehicles. It has been found that PCU for a 3 wheeler and 2 wheeler decreases with increase in their proportions whereas for bus it increases with increase in proportion of bus in traffic stream. It is also observed that PCU for 3 wheeler and 2 wheeler increases with increase in rate of discharge where as that of bus shows a decreasing trend. iv A mathematical equation to calculate PCU factors at N equal to 1.0 vehicle per second of green time has been established and correction factors have been suggested to determine PCU factors at any other value of 'N'. A relationship has been developed to calculate percent reduction in saturation flow due to presence of right turning vehicles at the intersection. Further equivalency factors for right turners at different radii of turn have been established and it has been found that one right turn vehicle is equal to (1 7.68/R) straight through vehicle. Further study has been recommended to extend the concept of dynamic PCU for different vehicle types and equivalency factors for right turners to some more infersections varying in geometric, traffic and environmental conditions before generalising the results.