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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 an enormous effect on traffic system. At present the traffic signal system in Dhaka city cannot manage this traffic. The traffic density has exceeded saturation level in most of the arterial roads.
Kakrail intersection and Shapla Chattar intersection have been used in this research study. Some important aspects which have been prompted in selecting these intersections are: a) Kakrail intersection is one of the busiest intersections in southern part and major arterial road has been pass through this intersection. Shapla Chattar is the intersection which is situated in the most renowned commercial area in Dhaka city; b) A comparison will be shown with respect to performance evaluation parameters between these two intersection which are god example of cross and controlled roundabout respectively; c) Huge congestion has been seen in these intersections in southern part of Dhaka city throughout the year which is one of the most important concerns for evaluating the performance of these intersections; d) In previous years many major road accidents were conducted in Kakrail intersection especially a student from the very near school named Wills Little Flower school had been died in 2010 under a bus closed by; e) Non lane based heterogeneous traffic is common phenomena in Dhaka city, but this heterogeneity has been widely seen in these intersections. So how this heterogeneity impacts the performance especially delay in these intersections is important concern.
Video camera was used to collect field data because it provides permanent record of data with minimum manpower and data collection is much more superior to manual data collection. Recorded film was replayed in the laboratory and required information for saturation flow and delay estimation was retrieved.
Analysis has revealed that at Kakrail intersection maximum discharge is 2389 PCU/hour and 1805 PCU/hour at Shapla Chattar intersection. Comparing 10 hours’ data, the highest discharge is occurred from 2:00 pm to 6:00 pm in Kakrail intersection and 8:00 am to 12:00 pm at Shapla Chattar intersection. The average discharge at Kakrail intersection is 2267 PCU/hour and at Shapla Chattar intersection is 1494 PCU/hour. The most dominating vehicle is rickshaw/van and on average 37.54% of total vehicles in 10 hours is passing through the Kakrail intersection. Similarly, in Shapla Chattar intersection most dominating vehicle is car/taxi and on average 24.20% of total vehicles in 10 hours’ data.
Flow fluctuation analysis has showed that in Kakrail intersection the major vehicular movement is occurred from Shantinagar to Kakrail and it is 37.94% about of total movement. In Shapla Chattar intersection major movement occurs from Fakirapul to Shapla Chattar approach and it is about 38.20%. Signal Cycle time and green time are obtained from field. In Kakrail intersection The cycle time in morning and evening peak hour is 130 sec and 223 sec respectively. In Shapla Chattar intersection The cycle time in morning and evening peak hour is 148 sec and 142 sec respectively. However, green time varies from phase to phase.
In order to assess delay incurred at the junction as well as to make the junction operation by signal, in this study attempt has been made to design traffic signal in a systematic way. The first widely used approximate delay formula was developed by Webster (1961) and Miller (1968) formulas are used to calculate the delay. In addition to assess the impact of heterogeneity on delay, Modified Webster Formula (et. al. Hoque, M.S. and Imran, M.A.) has been used. At Kakrail intersection max total average delay by Miller’s, Webster’s and Modified Webster’s formula is 237.87sec, 242.82sec and 300.55sec respectively. Similarly, at Shapla Chattar intersections max total average delay is 51.64sec, 50.47sec and 75.78sec respectively.
On the basis of average delay Level of Service of different approaches of these intersections at different time period has been determined according to Highway Capacity Manual. Worst case scenario for Kakrail intersection is at evening peak period and for four different approaches, it is E, F, E, F respectively. For Kakrail intersection worst case scenario is also at evening peak period and for two signalized approaches LOS is D and D respectively.
Other noticeable physical deficiencies of the studied junctions are faulty location and geometry of existing pedestrian crossing facilities and water logging problem. These need to be corrected and shifted to enhance handling capacity of the junction. The operational deficiencies that are mainly observed is the road side frictions in the form of parking activities by buses and para-transits as well as pedestrian occupancy in the active road which are reducing the effective width of the approach roads and eventually restricting the discharge capacity of the junctions. These also need to be control for further augmentation of overall junction capacity.