Calcutta, Oct. 10: Calcutta's longest flyover had to be turned into a one-way road from EM Bypass to Park Circus just a day after its belated inauguration because the administration had failed to estimate the traffic load and put safeguards in place.

After a day of chaos on the flyover, the police threw both the flanks open for Park Circus-bound vehicles this evening, forcing those headed the other way to take the connector below.

The key problem is that the 4.3km structure, thrown open yesterday, is still incomplete despite overshooting its original schedule of August 2012.

It's yet to get the two additional arms near the Park Circus end that will connect it to the AJC Bose Road flyover, so that all its westward traffic doesn't need to descend on the seven-point Park Circus crossing.

That's exactly what the traffic did yesterday and today, choking large swathes of south Calcutta till the 7pm quick-fix partially improved matters.

Police said the "experimental" one-way arrangement would continue for now. A police officer said a proper assessment could be done only on Tuesday. "Sunday and Monday (Mahalaya) are holidays. We can find out whether this system will work only on Tuesday," he said.

"We are only allowing Park Circus-bound vehicles to ascend the flyover. EM Bypass-bound vehicles from Park Circus are taking the old route through Suhrawardy Avenue, Darga Road and the Park Circus connector," another officer said.

The officer added that the one-way arrangement was helping spread the traffic a little thinner on the flyover, easing the queue and allowing faster dispersal through four lanes instead of two.

"Ordinarily, just two vehicles can come down the flyover's narrow Park Circus end at a time. The one-way system frees up two more lanes for simultaneous descent," he said.

In the afternoon, the flank for the city-bound westward traffic had been clogged by cars, much like yesterday. The police were therefore forced to intermittently stop vehicles from taking the flyover from EM Bypass.

Engineers who have specialised on traffic said the mess reflected the administration's poor understanding of the possible impact of the flyover's inauguration which, ironically, now seems premature despite the three-year delay.

Several of the engineers estimated that 2,200 small cars can cross the flyover through one flank in an hour while travelling at optimal speed in normal times. The one-way arrangement therefore created room for 4,400.

"We estimate that nearly 6,000 small cars were travelling towards Park Circus in an hour during the peak period," said an officer of the East traffic guard, managing the chaos at Park Circus around 8.30pm.

Experts were unanimous that the flyover should not have been opened to traffic without the additional arms.

"When an intersection has the potential for overcrowded traffic, four additional roads need to be built - something in the shape of a clover-leaf flower," said a traffic planning expert. "The problem here is that no provision was left for draining out vehicles."

He said that whatever "experimental measures" are taken to reduce the traffic snarls, the problem cannot be solved fully until the two links are ready.

An official of the government arm Calcutta Metropolitan Development Authority acknowledged that the two links had originally been scheduled for completion together with the main trunk of the flyover.

"Since most of the Park Circus-bound vehicles take the AJC Bose Road flyover, the arms were necessary," he said.

Calcutta had suffered from similar myopic urban planning when the state government dropped plans to build a ramp linking the AJC Bose Road flyover to Sarat Bose Road and another connecting the Park Street flyover to Mayo Road.

The AJC Bose Road flyover now has a ramp leading to Theatre Road but it was added only after the flyover had become operational and hundreds of thousands of commuters faced months of inconvenience.

This evening, vehicles climbed onto the flyover from EM Bypass through the designated flank for westward traffic but some of them subsequently changed flanks, with the police removing some of the guardrails to allow them to cross over.

The flyover project had been sanctioned in 2009 but was delayed because several state government agencies failed to cooperate.

Construction firm HCC could not lay its hands on the land for a long time as the civic body dilly-dallied on shifting its drains and underground water pipes and the police refused to allow barricades along the roads.

Serial letters from the company failed to stir the government. Work took place only in patches.

The project then came to a standstill for 14 months after the Mumbai-based company submitted a cost escalation demand in January 2013 and the Calcutta Metropolitan Development Authority refused.

In March last year, the company moved court, arguing it couldn't work because it hadn't got the entire land yet. The following month, Calcutta High Court worked out a solution.

It divided the project into two components, setting a July 2015 deadline for the flyover's trunk and allowing 12 more months to build the links to the AJC Bose Road flyover after the company said it had been unable to work for two years.

Sources said a realistic target for the links' completion would be Puja 2017 although state urban development minister Firhad Hakim has asked the builders to do it by Puja 2016.