01660160

Component

Traffic is heterogeneous in all countries in the world including US but the degree of heterogeneity is different in developing and developed countries. The Highway capacity manual (HCM 2010) of US has defined two categories of vehicles visually car and heavy vehicles. However, in the car category there are many models like hatchback, sedan, SUV and XUV are plying on the road whereas in the heavy vehicle category, bus, two and three axle trucks are there on the roads. The operating and physical characteristics of these vehicles are different and they affect the speed flow characteristics of the stream at different flow levels thus consequently affect the capacity of the roadway. The present paper demonstrates the effect of traffic mix on the capacity of urban arterial roads and proposes a mathematical model to determine the capacity of six-lane divided urban arterial at varying compositions of vehicles present in the traffic stream. Microscopic simulation software VISSIM is used to develop the model. Speed flow characteristics of various categories of vehicles are studied in the field and are used to calibrate and validate the model for mixed traffic conditions. Traffic data collected in the field are used to derive capacity of the road in terms of equivalent passenger car unit (PCU) per hour. The capacity of six-lane road as achieved from the field data is 6300 PCU/hr for one direction of traffic flow. This capacity value was further achieved through simulation run for ‘all car’ conditions using calibrated VISSIM software. The program was run for small car and one of the remaining four categories of vehicles at different compositions in the traffic stream. Regression equations were developed for each set of simulation run for all four categories of vehicle along with the standard car. These equations are then combined to develop the capacity model. Further, a stream equivalency factor (SEF) is developed that can be used to convert heterogeneous traffic stream into homogeneous equivalent without actually using the passenger car units (PCU) values. The proportion of each category of vehicle in the traffic mix and the total traffic volume (in veh/hr) are taken as independent variables in developing SEF model. Two models have been proposed in the study. The capacity model may be used for quick estimation of volume to capacity (v/c) ratio which is a surrogate measure of level of service (LOS) on the roadway. At the same time, the capacity of a roadway can be determined in pcu/hr using SEF model without actually using the PCU factors. Similar models can be formulated in developed country’s context where a variety of vehicles is present in the traffic stream.

This paper was sponsored by TRB committee AHB40 Standing Committee on Highway Capacity and Quality of Service.

18-01922

English

20p

2018

Transportation Research Board 97th Annual Meeting

Digital/other

Figures; References; Tables

Arterial highways; Highway capacity; Multilane highways; Traffic flow; Traffic speed; Vehicle mix

Highway Capacity Manual 2010

Highways; Operations and Traffic Management

Transportation Research Board Annual Meeting 2018 Paper #18-01922

TRIS, TRB, ATRI

Jan 8 2018 10:28AM