DYNAMIC PCU AND ESTIMATION OF CAPACITY OF URBAN ROADS

Abstract

The rapid pace of socio-economic development in India has made a significant impact on the traffic on the urban roads. On the other hand, the variety of modes has not reduced. Vehicles ranging from power driven fast moving type to man or animal driven slow moving type share the same road way space without any physical segregation. The vehicles which are less efficient cause operational difficulties to other vehicles. As a result congestion starts at traffic volume well below the capacity prescribed for that road. This happens mainly due to assumption of static PCU values to convert mixed traffic flow into homogeneous one which over estimates the capacity. Various agencies in India, like CRRI, IRC have recommended PCU factors for different categories of vehicles, which are derived for static conditions of traffic and roadway geometry. It has been emphasized in the literature also that PCU value is not static but depends on multitude of factors. In the present study, on attempt has been made to establish dynamic nature of PCU by analysing the data at four midblocks of New Delhi. It has been found that speed,traffic volume and its composition and road width are important parameters affecting PCU values. Variation in PCU values of different vehicle types with these parameters has been studied. The curves drawn to show the variation of PCU with traffic composition indicates that PCUr for -- vehicle type decreases with increase in its proportion in traffic stream. PCU for vehicle type increases with tra 111 volume level but the effect is not uniform for all vehicle categories. Further road width has inverse effect on PCU for vehicle type which has been explained on the basis of more freedom to monoeuvre at wider roads. Capacity of road was determined using the enveloping curve technique developed at CRRI, New Delhi. Speed flow relationship was used to determine the maximum flow of traffic. It has been shown that capacity of a 10.9 m wide road is 7000 PCU pH when static set of PCU values as- srrgg-ested- by -LRC was used and 4500 PCUpH when PCU values developed in this study were used. Capacity of other sections of roads have also been determined using dynamic PCU factors. Further, study has been recommended to extend the concept of dynamic PCU to roads having different geometric and traffic conditions before generalizing the results. iv