Abstract
The present study demonstrates the influence of operating speed on capacity of a midblock section of urban road. Speed–flow data collected at 12 midblock sections of 6-lane and 4-lane divided urban arterials in four metropolitan cities of India are analyzed to determine their capacity. Lane capacity was found to vary from 1482 to 2105 PCU/h. This variation is explained on the basis of city size and driving behavior, which would influence the free flow speed on the road. Free flow speed was also measured at each section and these speed data were used to determine operating speed 85th percentile of free flow speed of standard car) on the road. Lane capacity was found to be strongly related to operating speed on a road and a second-degree polynomial model is developed between the lane capacity and operating speed. This model is further validated by collecting speed flow data at two new sections and their capacity was estimated from field data and from the model developed in the study. The predicted capacity was found to be matching with field capacity and the maximum error was 0.10 percent. Operating speed on a road can vary due to road surface condition, side friction or similar other factors. All these will have influence on capacity of the road. The capacity model suggested in the present study can be a useful tool to determine capacity of an urban road from its operating speed data.
Highlights
Urban roads are defined in different manners in different countries
Due to long distances between the intersections and larger speed differential amongst vehicles, platoons get dispersed in the midportion between the intersections and the midblock section typically operates similar to a suburban section but with mixed traffic of urban characteristics
A relation was developed between traffic speed, flow and density under various rainfall conditions on urban roads in Hong Kong and found that capacity reduced by 22 percent from dry to heavy rain conditions whereas free flow speed reduces by 10% [10]
Summary
Urban roads are defined in different manners in different countries. An arterial in the United States is often characterized by a series of signalized intersections at close intervals and high density of access points [1]. Capacity of a midblock section will be important when grade separations are provided for through traffic on signal controlled intersections on an urban arterial. Traffic stream models, relating speed of vehicle type with flow and percentage of slow moving vehicles, were developed for each vehicle type. A study conducted on curved section of 2-lane highways to develop the regression models to predict operating speed. The present study was taken up with the objective of determining midblock capacity of urban arterial roads in different cities of India having no side frictions. These capacity values are found to be different in different cities and across the sections in a city. A strong relation is found between the lane capacity and operating speed on the road
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