20-11-2012, 06:01 PM
Performance evaluation of grade separation facility on energy conservation in traffic at major intersection in Chennai
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ABSTRACT
Major road junctions in Indian cities suffer from inadequate and inefficient traffic control system which invariably results increased delay and road accidents. Due to increase in delay and congestion at most of the intersections there has been a great loss to the society in terms of time loss in waiting at the intersections and the excess fuel consumed by motorised vehicles. A possible remedy is to separate the intersecting roads by levels in the form of grade separated intersections.
Grade separation is the highest form of intersection treatment. Grade separation facilitates smoother traffic flow with, reduced fuel wastage, least delay and traffic conflicts The code for grade separator design has to be evaluated whether it suits for our heterogeneous traffic system as it operates very differently compared to homogeneous traffic systems. Hence the codal parameters have to be evaluated whether they suit for traffic flow characteristics of current grade separation criteria like acceleration and deceleration lane and spacing between two grade separators. These criteria’s were studied and analysed in detail. The study was carried out at four intersections in Chennai. The study has been taken up with the various objectives such as to study the location aspects, form of grade separator, traffic characteristics, traffic movement and accident history of the study intersection. The benefits such as reduction in delay, fuel cost and accident was quantified to evaluate performance of grade separators.
Keywords: Transyt, fuel cost, flow characteristics
I. INTRODUCTION
The rapid growth of vehicle population has been causing a strain on the existing urban services[1] and infrastructure, for want of expansion and better management. The total number of motor vehicles in Chennai city has increased from 5.69 Lakhs in 1991 to 27.73 Lakhs in 2008. Motor vehicle population has increased at a phenomenal growth rate of 9.7% per annum during the last few decades. As per study on Traffic & Transportation policies and strategies in urban areas in India, the trend of growth of motor vehicle population in Chennai city is shown in Figure1 and composition of vehicle population of Chennai city for the period 1984
II. ESTIMATION OF DELAY
Delay is a common phenomenon occurring at signalized intersection. Seldom one passes through all the intersections without delay of atleast few seconds. Delay at a signalized intersection means, the average delay caused to the vehicles at the signal due to various factors like traffic flow characteristics, vehicle type, timing of signal phases and cycle length. Delay is estimated in this study .
By field observations, using Webster’s model and delay model in TRANSYT software. The delay is estimated for the study intersections with and without grade separator for the year 2009.The flow through the grade separator is substituted in equivalent arm to find the delay without grade separator.
A.1 FIELD MEASUREMENT OF DELAY
Vehicle arrival time and vehicles leaving time at each arm of the intersection is recorded for every 10 sec interval for duration of 2 hours. The aggregate delay is arrived and the average stopped delay per vehicle in terms of sec/vehicle was computed.
Delay Estimation Using TRANSYT
Delay model in TRANSYT[4] estimates uniform delay by integrating the number of queued vehicles over the entire cycle, with a queued vehicle defined as one that is not moving at cruising speed. This method explicitly takes into account the effects of progression (via simulation). Total delay to traffic on a link is the sum of the delays to all the individual vehicles using the link during a period of time. Total delays are usually quoted in units of PCU-hours/hour. Similarly, the total delay rate in a network of signals can be considered as the sum of the average queues at all the stop lines. Three types of delay namely Uniform delay rate, Oversaturation delay rate, Random delay rate can be calculated using TRANSYT.
A link on which traffic arrivals do not exceed capacity is called the uniform delay rate. Links where traffic arrivals exceed capacity, the traffic queue increases each cycle by the amount by which arrivals exceed departures throughout the period of oversaturation is called the oversaturation delay. A further element of delay not accounted for in the uniform delay calculation is that due to variations in traffic arrivals from cycle to cycle. This is known as random delay. Figure 3 illustrates, for a particular case, the way in which the three delay elements (uniform, oversaturation and random) vary as the degree of saturation on a link increases.