Flow Relationship and Capacity Estimation on SH-41 Civil Engineering Project Report
Highway capacity values and speed-flow relationships used for planning, design, and operation of highways, in most of the developed countries, have been based on Manuals and Codes of practices, which are valid for fairly homogeneous traffic comprising vehicles of more or less uniform static and dynamic characteristics. Even under nearly homogeneous traffic conditions, it is necessary to convert heavy vehicles such as buses and trucks, which constitute a small proportion of traffic, into equivalent numbers of a standard type of vehicle (usually passenger cars) to measure the traffic flow using a single unit. The road traffic in most developing countries such as India comprises vehicles of wide-ranging physical dimensions, weight, and dynamic characteristics. Also, the motorized and non-motorized vehicles share the same road space without any segregation. The speeds of these vehicles vary from about5 to over 100 km/h. Due to the highly varying physical dimensions and speeds; it becomes difficult to make the vehicles follow traffic lanes. Consequently, they tend to choose any advantageous position on the road based on space availability. Also, the extent of vehicular interactions varies widely with variations in the traffic mix. Vehicles, which are less mobile in terms of
maneuverability, cause a significant level of friction to themovement of other vehicles in the traffic stream. The extent of friction realized by the different categories of vehicles depends on their static and dynamic characteristics. For example, at higher traffic volumes a large proportion of motorized two-wheelers and bicycles may be able to move with speeds closer to their free speeds because of their ability for utilizing smaller gaps in the stream for movement, while the large-size vehicles such as buses and trucks may be subjected to considerable speed reduction. Traffic engineers account for the impact on capacity from the different types of vehicles by assigning each class of vehicle a
passenger car equivalent (PCE or PCU) value. This value represents the number of passenger cars that would consume the same percentage of the highway‟s capacity as the vehicles under consideration under prevailing roadway and traffic conditions. This study deals with the development of a simulation model to replicate heterogeneous traffic flow on
urban roads of developing countries such as India and the application of the model to derive PCU values for the different types of vehicles in heterogeneous traffic streams and hence arrive at capacity standards.
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