The present study provides a methodology for identification of the conflict zone between a turning vehicle and on-coming vehicles at uncontrolled median openings on urban roads under mixed traffic conditions. Data for turning movements of different types of vehicles were collected at 13 median openings on 6-lane roads and 8 median openings on 4-lane roads in different cities of India. These data are analyzed statistically and it was found that the critical position (path of the outer wheel) of a vehicle is influenced by the vehicle size and the road width. In the case of 6-lane roads, the critical position of turning vehicle may follow a unimodal or bimodal distribution depending upon the proportion of motorized two-wheelers (2-W) in the turning volume. On 4-lane roads, the gamma distribution was found to fit the placement data at all the eight sections. A simple model is proposed to identify the boundary of the conflict zone at median openings. The geometrical augmentation required at the median opening in order to avoid the conflict between turning vehicles and through traffic in the opposing median lane is also suggested.
This paper proposes a practical approach to estimate the conflicting traffic volume caused by U-turns at uncontrolled median openings under mixed traffic conditions. Data were collected at 21 median openings on multi-lane divided roads in India (i.e. 13 on six-lane and eight on four-lane). The road width at the median opening is divided into three parts: zone of severe conflict, zone of safety and unaffected zone based on the placement of the left wheel of U-turning vehicles (left-hand drive rule followed in India). The first two zones together are considered as the conflicting zone for calculating the conflicting traffic. The proportion of opposing through traffic within the conflicting zone is considered as the conflicting traffic volume for U-turns. The conflicting volume at all the sections is estimated based on placement of through traffic across the width of the road and it is found to be dependent on the size of the U-turning vehicle. An equation is suggested to calculate the conflicting traffic based on the composition of U-turning traffic. The conflicting traffic on six-lane roads is found to be relatively, low but on four-lane roads, almost all of the opposing traffic becomes conflicting traffic for U-turns.
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