Effectiveness of vehicle actuated signals for at grade four legged intersections in Sri Lanka : a comparison study against time traffic signals

Abstract

The goal of traffic engineers in recent years is trying their best to get the most out of the systems that they develop. By designing efficient systems, using the advancement of electronics and Information Technology (IT) the overall costs of transportation should be easier to manage. Road Development Authority under the Ministry of Ports and Highways administrates over fifty traffic signals in the Western Province of Sri Lanka. All these fixed-time traffic signals are primarily located at major routes of the city of Colombo and other townships linked with Colombo in the Western Province. In Sri Lanka, it is anticipated that the prevailing fixed-time traffic signals would be replaced by modern Vehicle Actuated signals, which would be the next generation of traffic signals possibly be introduced in near future. This study has been carried out to evaluate the efficiency of vehicle-actuated signals against prevailing fixed-time traffic signals, prior to their implementation in Sri Lanka. This study was carried out to compare the efficiency of Vehicle Actuated Signals against prevailing fixed-time traffic signals in an urban area. Several signalised intersections were carefully studied with their geometric and traffic turning movements especially in Colombo (the capital of Sri Lanka) region and a simulation was programmed in Microsoft Excel in such a way to represent traffic turning movements of typical intersection in urban area. Various traffic volume combinations were selected among North-South and East-West through traffic and other turning movements (Left-turns, Right-turns & Heavy vehicles) were randomised within their permissible limits (found from the analysis of existing junctions) to characterise a real dynamic situation at an urban intersection. Numerous calculations for Cycle time, Vehicle-delay, Pedestrian-delay and Critical movements of different traffic combinations were computed with the help of a well-known Australian Software called SIDRA [Signalised (and unsignalised) Intersection Design and Research Aid, developed by Akcelik & Associates Pty Ltd]. The outcomes of analysis were tabulated against each different traffic combinations produced by Excel simulation and were compared in graphical and tabular forms for the efficiency of fully-Actuated Signals against fixed-time Signals. It is found that the replacement of fixed-time traffic signals with fully actuated signals for stand-alone intersections shall not produce any major enhancement (reduction in delay) to the existing at grade four-legged intersections, which have three standard-approach lanes including right turn-bays with optimum length and two standard-exit lanes. Moreover, it is sensible that semi-actuated signals would be a better alternative for signalised intersections, where major roads (continuous high demand) meet with minor roads (very stochastic or very low traffic demand).