STUDY OF TURNING SPEEDS AT UNCONTROLLED INTERSECTIONS

Abstract

The most critical movement in the uncontrolled intersections is right turning movement. According to IRC-SP-41-1994 there is about 12% right-out and 30% right-in collisions of the oncoming vehicles, 9% right-out and 15% of right-in collisions between following vehicles and 22% collisions between two turning vehicles. So there is a need study the turning speeds at the uncontrolled intersection, specially the parameters influencing the turning speeds. The higher are the vehicle turning speeds, bigger is the challenge to pedestrians. The pedestrian's path also gets affected by the design of the corner. The selection of radius is weighed in the light of these effects and may result in a compromise in pedestrians need and vehicle speeds. The approach lane width and exit lane width are also parameters which affect the vehicle speeds and safety of road users. Right turning traffic affects capacity and traffic delays, and causes safety hazards and driver confusions. In Indian condition where, heterogeneous traffic is there, the conditions become worse for the vehicles and pedestrian. Generally, vehicles slow down on the approach and in the initial portion of a left and right turn with slowest speeds near the middle of the turn. Therefore the speed predicted for a pedestrian crossing needs to consider whether that crossing is at the beginning of the left and right turn or near the middle of the left and right turn. For the study of turning speeds at uncontrolled intersections, data collected and analyzed of four Y or T-junctions and two four legged intersections i.e. 16 left and right turns. The uncontrolled intersections are analyzed for two conditions, first are analysis of normal traffic speed data and second are analysis of interference of traffic speed data. We observed uncontrolled intersections for overall, Y or T-junction and 4-legged intersection condition for both left and right turning. In the normal case the effect of turning speeds on turning length, sight distance, approach lane width, corner radius and number of lane for five types of vehicles for both left and right turn are observed. In the case of interfering of traffic speed data analyzed by predicting equations for five types of vehicles which shows the relationship between percent reduction of speeds and number of interfering vehicles at different distances for both left and right turn. The equations of mean speeds for different types of vehicles are predicted for both left and right for T or Y-junction and four legged intersection. Validity of results is checked by using Nayeem's speed data of three intersections. The intersection sight distance varies with turning speed, i.e. intersection sight distance is directly proportional •to design speed. Turning radius is also directly proportional to design speed. Acceleration is also directly proportional to sight distance. Turning length is also directly proportional to turning speed. We observed the interfering vehicles at 0-9m are more affecting on mean turning speed of vehicles. Regression analysis show that effect of interfering vehicles in distance band 0-9m, varies between 2 and 3 times of that in 9-12 in. From the regression analysis it is observed that for left turn at Y or T-junction for all types of vehicle bicycle, two-wheeler, car, bus, and truck; corner radius is more significant than sight distance, for right turn it is observed that, for all types of vehicle bicycle, two wheeler, car, bus, and truck; sight distance is more significant than corner radius. From the regression analysis of left turn at four legged intersection it is observed that; for all types of vehicle bicycle, two wheeler, car, bus, and truck; sight distance is more significant than corner radius, for right turn it is observed that; for bicycle, two wheeler, bus, and truck; sight distance is more significant than corner radius; and for car corner radius is more significant than sight distance. Keywords: Turning speed, Sight distance, Turning length, Lane width, Corner Radius, Traffic volume. iv