A standard city should have 25 per cent of its total space for road infrastructure. But Dhaka has only about 7.5 per cent. Given the very high population density in the capital, the space requirement for road infrastructures should be much higher than a standard city's requirement. Moreover, for efficient and unhindered traffic movement, adequate road spaces are prerequisites, based on functional classification of roads.
In urban areas, the functional classification of roads is broadly categorised into: (1) arterial road (known as main road), (2) collector/distributor road (it collects traffic from local roads, then feed those into arterial roads and vice versa) and (3) local roads (lowest hierarchy roads for access to houses). But ruefully, the road classification (for urban roads) based on hierarchy is absent in Bangladesh. Thus, it is also liable for unplanned city development that has resulted in relentless gridlock and road safety problem.
Every plan should be carefully weighed in all phases while in many cases, this issue triggers controversies in the post-implementation stages, for example, Mohakhali flyover and the link-road demolishing Rangs Bhaban. This is really a poignant issue as the developed countries always ensure best investment with meticulous planning. That is why they have attained the prestigious status.
For addressing gridlock problem, not only capacity augmentation of arterial roads is necessary but also proportionate capacity augmentation of collector roads and local roads is also absolutely essential. In fact, the flyovers are for capacity augmentation of arterial roads only in the form of grade separation as there is no space at the ground level. But unfortunately, everyone is concerned about gridlock problem on the arterial roads (main roads) but no one has yet pointed out the dire consequences of disintegrated capacity enhancement of arterial roads without proportionate capacity enhancement of collector and local roads.
Traffic dissipates from arterial to collector and then is redistributed to local roads and vice versa. Therefore, the unilateral capacity enhancement of arterial roads by constructing flyovers would result in much quicker traffic arrival at the interfaces of collector and local roads. Thus, the collector and local roads would endure much more traffic, particularly at peak-hours due to reduced travel time on arterial roads as compared to the present situation. This situation would spell further mess on the collector and local roads as many of such roads are already experiencing capacity failure. Therefore, proportionate capacity augmentation of collector and local roads is also absolutely necessary to maintain equilibrium in the total network. Otherwise, it would just be a transfer of current logjam problem from arterial roads to collector and local roads. Therefore, another impasse in the road traffic condition is supposedly lurking that would surface immediately after the completion of flyovers, particularly where flyovers would land on busy areas.
Moreover, flyovers are constructed narrowing the existing roads, in many cases, both at starting and end points due to non- acquisition of adjacent lands causing bottleneck. Thus it would adversely affect traffic movement, even those not using flyovers. In addition to that, flyovers' large piers (the vertical structure on which flyover rests) have reduced pave-width in many cases. Thus, they have further reduced the road-spaces which have already proved to be inadequate. But modern structural engineering technologies could have addressed this issue effectively.
Furthermore, the flyovers terminating at the busy locations are almost ubiquitous in this city. These might cause road safety problems and chaotic situation by two grade-separated traffic while joining together at ground level due to differential speed between them as the vehicles on flyover are expected to have higher speed. Besides, faster the traffic would cross flyover section, the more traffic jam might result at end-points. Accordingly, imposition of mandatory slower speed-limit might be necessary on flyovers to lessen the chaotic traffic situation at the downstream ends.
For safe movement on flyover section, the guardrail systems should have adequate strength to sustain the impact of errant vehicles and safely redirect without creating serious snags or overturning of the vehicles. In addition to that, if guardrail system is not strong enough for heavy vehicles, then promulgation is required to this effect that these vehicles must avoid the outermost lane (the lane adjacent to guardrail system) and highly retro-reflective materials (worthy for day or night, wet or dry) should be used for signing and marking. Besides, effective mechanisms should be incorporated to reopen it in the shortest possible time should there be any accident.
Moreover, if pedestrians' sidewalk is considered, then the design should be safe enough both for pedestrians and vehicles so that errant vehicles should not leapfrog onto the railing or roll-over. The pedestrians' safety considerations should not be neglected as in Mohakhali flyover where pedestrians' safety has been disregarded in favour of vehicles.
Another crucial issue for an efficient intersection/junction operation is that it must be in harmony with the total capacity of roads linking that intersection. Therefore, it is apprehended that the flyovers being constructed to enhance the capacity of existing arterial roads without capacity augmentation of associated intersections/junctions would end up in a counterproductive result - for example, the logjam problem at the Kakoli intersection (particularly while moving towards Farmgate and Tejgaon) which stems from capacity mismatch between intersection and roads feeding the intersection. Several flyovers have been constructed to enhance roads' capacities while the capacity of Kakoli intersection remains unaltered. Thus this has resulted in capacity failure leading to logjam problem. Therefore, if the capacity of a link be increased, then the capacity of the associated intersections/junctions should also be duly addressed.
In this context, it is very relevant to mention here that modern technologies like software tools and modelling techniques should have been used, such as, aaSIDRA software that could be a guide to precision capabilities rather than current practice of plausible results.
What is of more concern is that the construction of flyover might encourage booming of motorised traffic. All vehicles would require descending on ground level while returning back home. Therefore, the inflated traffic would further aggravate the existing gridlock problem in the city.
Nevertheless, flyovers have brought a great relief in several cases that provide direct ingress or egress facilities averting all road traffic impediments plaguing the city, for example, the Gulistan-Jatrabari flyover (though the toll is a burden on the poor classes of people). This flyover should have been constructed with the provision for mass transit system like Bus Rapid Transit (BRT) that requires exclusive-lanes. This is a crucial issue to encourage out-migration from Dhaka city towards greater Dhaka area and to re-develop in the form of conurbation.
The real solution lies in capacity enhancement of all hierarchical roads and intersections. Unilateral capacity augmentation of arterial roads might cause another misery. Hence, all these factors should have proportionate and well-integrated consideration to achieve efficacious results.
The writer is a road safety and transport engineer.
 himu120@yahoo.co.nz
Assessing impacts of flyovers
Md Shamsul Arefin | Published: January 24, 2015 00:00:00 | Updated: November 30, 2024 06:01:00
Kuril flyover
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