CAPACITY ANALYSIS OF URBAN ARTERIAL ROADS UNDER MIXED TRAFFIC CONDITIONS

Abstract

Urban roads in India are classified either on the basis of the number of lanes provided within an undivided or divided cross section or in accordance with their functions in the total urban road network. Besides the freeways and expressways, urban roads in India are classified into the following four main categories; Arterial, Sub-arterial, Collector street, and Local street. An urban arterial is a general term denoting an urban street primarily for through traffic, usually on a continuous route. The arterials are generally divided multilane roads with full or partial access. The distance between intersections on an urban road is generally large but speeds are low due to mixed nature of traffic. Due to long distances between the intersections and larger speed differential amongst vehicles, platoons get dispersed in the mid portion between the intersections and the midblock section typically operates similar to a suburban section but with mixed traffic of urban characteristics. The present research focuses on traffic flow analysis on urban arterial roads and estimation of their capacity. The research is accomplished in three parts. The first part is estimation of passenger car units for the different categories of vehicles typically found on urban arterials during daytime and to study the variation in PCU with different traffic and roadway conditions. The second part includes development of speed-flow relations on 4-lane and 6-lane divided urban arterial roads in different cities of India and thereby to estimate their capacity under mixed traffic conditions. The third part of the research is focussed on quantification of effect of side frictions like bus stop and pedestrian cross-flow on capacity of urban roads. Field data were collected through videography on 6-lane and 4-lane divided urban arterial roads in five cities of India namely New Delhi, Jaipur, Chandigarh, Bengaluru and Thiruvananthapuram. All sites are grouped into two categories; one group consisted of locations on 4-lane and 6-lane roads with no side friction activity. These sites are termed as base sections. The other group consisted of the sites having one type of side friction activity like curbside bus stop or pedestrian cross-flow. Data extracted from the video were used to determine PCU of different categories of vehicles. Five different categories of vehicles were identified on the selected road a Abstract ii sections. These are small car (CS) or standard car, big car (CB), heavy vehicle (HV), motorized 3-wheelers (3W) and motorized 2-wheelers (2W). It was found that PCU values for different types of vehicles on 4-lane and 6-lane roads are almost same, and hence a single set of PCU values is suggested for both categories of urban roads. These values depend on traffic volume and traffic composition of the stream. To further simplify the use of equivalency factors, a new concept of Stream Equivalency Factor (K) is introduced in this research which is defined as the ratio of flow in pcu/hr and flow in veh/hr. This factor is found to be dependent on traffic volume and composition and mathematical relations are developed for estimation of K factor for 4-lane and 6-lane roads. This factor does not require use of PCU values for individual type of vehicle to convert a mixed traffic stream in to a homogenous equivalent. Field data collected on 12 sections of 6-lane and 4-lane urban arterial roads were used to develop speed-density and speed-flow curves and capacity of each section was estimated. It was observed that capacity of 6-lane roads varies from 1500 pcu/hr/lane to 2105 pcu/hr/lane, and that of 4-lane road sections varies from 1482 pcu/hr/lane to 2063 pcu/hr/lane. To further analyse this aspect of change in capacity with city size, free-flow speed (FFS) data of standard cars were taken at each site. These data were used to determine operating speed (OS) of the road section which is defined as 85th percentile FFS of standard car. The lane capacity was found to be related with operating speed on the road. Two types of side frictions; pedestrian cross-flow and curbside bust stops are also studied. Data were collected at six sections of 6-lane roads and three sections of 4- lane urban arterials with pedestrian cross-flow and speed-flow curves were drawn to obtain capacity of the sections. These capacity values are then compared with the base capacity of these sections. It was found that a pedestrian cross-flow upto 200 peds/hr does not influence capacity of the road, but higher pedestrian cross-flow causes reduction in the capacity. A second degree polynomial relation is developed between reduction in capacity and pedestrian cross-flow. Field data were also collected at six sections of curbside bus stops (three each on 6- lane and 4-lane roads). Forced lane changes (FLC) by other vehicles due to stopping of buses and total lane changes (TLC) in the traffic stream are taken as a parameter to determine the capacity loss. Curves are developed for estimation of capacity loss based on FLC in each count period. Further, a simple procedure is developed based on bus frequency and five minute traffic volume counts to determine reduction in capacity.