The effect of left-turning traffic on the performance of through traffic at a signalized intersection: case study of Anloga intersection in Kumasi, Ghana

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Rapid vehicular population growth in urban centres in developing countries such as Ghana has resulted in increased volumes contributing to long delays at signalized intersections. At intersections where there is high volume of left-turning traffic, spill back and blocking of the through traffic has much effect on saturation flows. In many situations, a change of layout of intersection or even grade separation may be the option for improving delay and LOS but uneconomical to most developing countries due to lack of funds or inadequate right-of-way or both. The objective of this thesis was to evaluate the effect of left turning traffic on delay to through traffic at signalized intersection, evaluate the effect of left turning traffic on saturation flow for through traffic at a signalized intersection and propose a left-turn storage lane length that will improve the saturation flow and reduce delay for through traffic at a signalized intersectionusing micro simulation tool (VISSIM).An intersection characterized by long queue and delays during peak periods was chosen as the study site. Two hours video data collection was undertaken on a typical morning peak from which the traffic demand and turning movements were extracted. VISSIM was used for simulation analysis of the intersection. The model was calibrated with the traffic flow, queue length and delay data for the approaches and the result validated. After conducting a sensitivity analysis by increasing the approach volume from 1000pcu/h to 3000pcu/h and varying the left turn traffic percentage and left turn storage lane lengths, it was revealed that as the approach volume of signalizes intersection increases with a corresponding increase in left-turning traffic volume proportions, delay to through traffic movement increases and its saturation flow reduces. It was also found out that, for approach volumes of 1000pcu/h to 3000pcu/h and corresponding left turn traffic proportion 10% to 20%, 150m optimal storage lane is required to reduce delay and improve on saturation flow. For an approach volume of 1000pcu/h to 3000pcu/h with 30% to 50% left turn traffic proportion, 175m storage lane is required to reduce delay and improve on saturation.
A thesis submitted to the Department of Civil Engineering, College of Engineering, in partial fulfilment of the Requirements for the Degree of Master of Science Road and Transportation Engineering.
storage lane, micro simulation., Saturation flow, delay, signalized intersection, left-turning traffic