Post evaluation of flyovers with adjoining road-network in Dhaka city

Abstract

This study has been undertaken with the aim of evaluating the current performance of at-grade road networks in Dhaka city present in the study network of partially grade-separated flyovers. Level of Service (LOS) was chosen as the primary measure of performance of the road network. In addition mobility and congestion levels were assessed to evaluate whether or not flyovers have helped its area of influence significantly. The identified road segments were treated as urban street segments or multilane highways, depending on their characteristics. Road segment performance was extensively evaluated across four periods of measurement, namely weekend day, weekend night, weekday day and weekday night. Traffic flow and related parametric data were taken at peak hour periods. Specifically, analysis was done to assess grade-wise space usage in study areas, assess traffic flow, assess roadway conditions, determine saturation flow rates, assess mobility conditions, determine level of service, assess pedestrian risk at level crossings and assess congestion level in study areas. LOS was shockingly found to be F at all considered urban street segments during all periods of measurement, indicating the worst possible traffic conditions. Flow-capacity ratio was found to vary between 0.28 and 11.84 at segment direction, indicating that present capacity of at-grade roads is insufficient to accommodate existing demand, which is expected to increase in future. Ratio of travel speed to free flow speed was found to vary between 0.02 and 0.29, while average travel speeds across entire facility of the study areas were generally found to hover around average walking speeds. It indicates that roads have very poor mobility. On the other hand, multilane highways were found to perform better, with LOS varying between A (best condition, free flow condition) to C (stable flow). In addition congestion analysis revealed that, congestion has generally increased over the years when compared with previous studies. Reconnaissance survey and detailed observations at both above-grade and at-grade road facilities have revealed several critical factors that significantly reduced road performance. Among these factors are uncontrolled street parking and random bus stoppage, which have decreased road capacity and contributed to high flow-capacity ratios and poor LOS rating. In addition, traffic demand has increased considerably in recent years, fueled by rising private vehicle ownership (cars, jeeps, microbuses, etc.). What is more alarming is that construction of flyovers without proper traffic regulations have acted as inconsiderate supply side policies, that have encouraged growth of private vehicles at the expense of public transit. If present traffic policies are allowed to continue and are not corrected, the temporary increase in capacity because of added grade facilities will worsen traffic congestion in the long-run, as shown using comparison with previous studies regarding traffic congestion. Congestion have even started forming above grade, which was not an occurrence two years ago. The root cause of the problem has been identified to uncontrolled and rampant growth of private vehicles. The study recommends that people’s choice of mode needs to be urgently shifted from private to public transit, which has been viewed as a perpetual solution in many countries around the world.