The city is going through a transformative phase with marked changes in lifestyles, consumption patterns and travel demands over the past decade. With regard to the most noticeable public infrastructure utility, namely the roads, tree-lined stretches have given way to a series of flyovers.

Now, with the announcement to build two four-lane grade separators along Anna Salai — one of the most important arterial roads in the city — the costs and benefits of a flyover-centric approach to meet the ever-increasing vehicular traffic capacity have come into prominence.

One of the grade separators, estimated to cost Rs.161 crore and spanning a length of 1.9 km, would come up between the P.Orr & Sons showroom, opposite the new Assembly complex, and the Spencer Plaza junction.

The other one, to be constructed at an estimated cost of Rs.339 crore, would be 2.9 km in length and stretch between Anna Arivalayam in Teynampet and the CIT Nagar First Main Road junction near Saidapet.

Chennai Metropolitan Development Authority (CMDA) has already allocated Rs.385 crore, collected under the infrastructure and amenities charges in the Chennai Metropolitan Area, for the project.

Susan Mathew, Vice-Chairperson, CMDA, said that piling work would have to be completed before March 2011 to avoid any conflict with the tunnelling work for the Metro Rail project. According to a senior CMDA traffic planner, as the volumes at the junctions on Anna Salai far exceed the threshold of 10,000 Passenger Car Units (PCUs) per hour, the measures to decongest traffic at “each junction warrants higher order solutions.”

K. Gunasekaran, assistant professor, Division of Transportation Engineering, Anna University, said there were three primary reasons to justify the construction of a grade separator. Apart from reducing vehicular emissions and the number of accidents, such facilities should help significantly reduce the waiting time or delay time at the junction. A decrease in delay time must also result in an increase in the average journey speed, which currently stands at 21 kmph in the city.

However, most existing flyovers have only shifted the problem to the next junction, Mr. Gunasekaran said, “as the reduction in delay time has been only marginal.”

N.S. Srinivasan, former Director of the National Transportation Planning and Research Centre, said that the capacity of any vehicular corridor depends on the efficiency of intersections. “A flyover must never be looked at in isolation. It must be planned as a network. Speeds on Anna Salai near the Thousand Lights Mosque during rush hour are as low as 5 to 6 kmph. The actual problem is that development has intensified along corridors without adding adequate reserve traffic capacity.”

Flyovers are only cosmetic measures to address the issue but not the solution, he said. “Intersections are important for the dispersal of traffic. The proposed grade separators must incorporate exit ramps near strategic junctions to have any significant impact.”

However, a senior official of the Highways Department said exit ramps cannot be provided “as there was no space to provide adequate ‘turning radius' and no foundation work can be carried out on either side of the median owing to the Metro Rail project.”

He added that the project also envisaged pedestrian amenities and proper footpaths on Anna Salai by expanding the available road space. A subway has also been proposed at Little Mount. The maintenance of the existing subways is likely to be entrusted to private agencies.

Despite various efforts in the past to streamline traffic on Anna Salai, the stretch has a high degree of congestion. A bus lane has worked, but it extends across only 2.5 km of the 15-km-long arterial road. The same has been the case with regard to pedestrian-friendly features such as pavements and subways, and the service lanes for slow-moving vehicles. The CMDA official said they are inadequate on account of commercial activity.

There is no continuous footpath along Anna Salai when compared to other roads such as Kamarajar Salai.

According to the traffic planner, efforts were under way to rectify the situation. Chennai Corporation and other agencies concerned have been asked to follow the norms while implementing projects to ease traffic congestion.

The traffic planner also underscored the need for the police to harness the potential of technology and work in close coordination with other agencies to come up with better solutions to decongest traffic on Anna Salai. One of the measures could be installation of Area Traffic Control System, under which right of way at intersections would be provided based on the volume of vehicles approaching them.

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