Deficiency of traffic signal control system in Dhaka city

Abstract

The widespread commercial, industrial, government, private and other activities have encouraged migration of people from outside resulting in abnormal growth of vehicular population in Dhaka City. The rapid growth of vehicular population is causing enormous effect on traffic system. At present the traffic signal system in Dhaka City can not manage this traffic. The traffic density has exceeded saturation level in most of the arterial roads. In this research, a total of 70 signalized intersections and 253 approaches in these intersections in Dhaka City were studied. Detail field surveys are conducted in each intersection. From survey of the existing signal system it is observed that out of 70 signalized intersections, 84% are fixed time (FT) multi-plan signal system, 9% are Centrally Monitored Vehicle Actuated Signals, 3% are pedestrian actuated and the remaining 4% are vehicle and pedestrian actuated control system. Field observation reveals that with the fixed nature of control system, often the prefixed timing plan does not match the demand of actual flow. Field observations reveal that only one timing plan is provided at 61 numbers or 87% intersections. It was also observed that among 70 signalized intersections, 1% signals are designed with 5-phase timing plan, 43% with 4-phase plan, 49% with 3-phase plan and 7% with 2-phase plan. Significant numbers of physical deficiencies are identified at the intersections. The placement of signal is wrong at 59% intersections, signal light direction is wrong at 27% intersections; controller cabinet conditions are not satisfactory in intersections. Access is restricted for the maintenance of signal at 21% intersections, size of mast arm is wrong at 84% intersections, pole and mast arm are colorless at 54 % intersections. Mounting of signal head in pole and mast arm is wrong at most intersections. Traffic sign and road marking provided at intersections are fewer than required. Pedestrians signal head is broken at 39% intersections. Footpath, pedestrian refuse, median conditions are not good at signalized intersections. Sight distances at intersections are very poor. Signals are not clearly visible at some intersections due to obstruction like as signboard or bill board, trees, electric pole etc. At 45 % approaches signals are not visible due to obstructions. Significant numbers of operational deficiencies are observed at the intersections. In old Dhaka at almost all of the traffic signals are not operational. Non- motorized vehicle are observed more in old Dhaka. Most of the intersections are controlled manually. Such as police control traffic manually by hand at 47% intersections, auto signal runs at 53% intersections. Both auto signal and police control by hand at 56% intersections. Maximum green time observed too long at some intersections and exceeds the maximum limits. All red phases, preemption, traffic control at special events and incidents management are absent in signal system at all intersections. Pedestrian signal conditions are very worse and road users do not follow. Pedestrian signal lights are off at 59% approaches. No pedestrian signal is found at 20% approaches. Signal retiming is not done properly and timely in most cases. Monitoring and maintenance are also very poor. There are no guidelines or manuals for signal operation and maintenance. Some cities of developing countries like Delhi, Pune, Bangalore, Bandung and Phuket use advance system such as Area Traffic Control System (ATCS), Phuket type, Central Control System for signal operation. In Dhaka City the signals are isolated, fixed time and manual control system. Deficiencies of Supporting TCDs are more in Dhaka city as compared to Delhi city. Physical deficiencies are observed largely in placement of signal, signal light, signal head, size of pole and mast arm, the access for maintenance of signal, pedestrian signal and signal visibility. The operational deficiencies are mainly observed in signal timing control, retiming, discipline or rules, maintenance of traffic signal, signal timing plan, preemption, traffic control at special events and incidents. Management practices, availability of a mission statement and annual review are absent. Ineffective operation, maintenance and monitoring of traffic signals have safety implications. Deficiency of traffic control device causes road traffic violations that have an adverse effect on safety.