The fate of the next phase of the Parama flyover lies tangled in a web of utility lines under Congress Exhibition Road.
Infrastructure company HCC has sought permission to dig a trench along the road, the first step towards building one of the two ramps that might allow two-way traffic on the flyover officially called Ma without causing long snarls.
A trench will enable engineers of the company map the underground utilities that need to be shifted for the project to commence.
Sources in the Calcutta Municipal Corporation (CMC) said there were at least five types of underground cables and pipelines along the length of Congress Exhibition Road - water and gas pipes, CESC and BSNL lines and the civic body's sewers and subsidiary electricity cables.
Shifting all these utilities is a near-impossible proposition without being certain of the layout, which is why HCC wants to map the network of lines first.
One of the arms of the Parama flyover connecting it to the AJC Bose Road flyover will run over Congress Exhibition Road. A brick sewer under New Park Street - between Bridge No. 4 and the Park Circus seven-point crossing - might also need to be removed, the sources said.
"Unless trial pits are dug, we can't figure out the layout of the utilities. Besides water and CESC lines, we have the Greater Calcutta Gas Supply pipeline and the CMC's streetlight cables to contend with," said a senior engineer of the HCC.
"Most of these utilities are on one side of Congress Exhibition Road and they need to be shifted to the other side before construction can start. The gas pipeline itself runs around 70 metres."
In a letter to the Calcutta Metropolitan Development Authority, the executing agency for the project, HCC has said that it cannot meet the high court's deadline of May 2016 unless access to the site is granted immediately.
The police want more time to chalk out a traffic plan for the snarl-prone area before allowing a part of the road to be cordoned off, even if it is to dig a trench.
Engineers said they would immediately require around 10 metres of road width, which the traffic police bosses fear would impede traffic flow in and around Calcutta's busiest crossing.
"The road is around 12 metres wide and we would need around four metres for single-lane traffic," a senior police officer said. "We must have space for at least a bus to travel in one lane because this road is the only option for vehicles heading towards Gariahat in the south or taking the AJC Bose Road flyover."
A suggestion to create space by reducing the width of the pavement along Congress Exhibition Road won't be possible unless all utilities are shifted to one side of the road from their present location, HCC engineers said.
This would have to be done along the entire stretch from Congress Exhibition Road to AJC Bose Road, with Nasiruddin Road in between.
Once all the utilities are shifted, HCC would barricade 8.5 metres of the road width to start raising 32 pillars along the stretch from Congress Exhibition to AJC Bose Road, where the city's longest flyover is supposed to merge with the one that used to hold that record until recently.
The challenge of shifting underground utilities has delayed another infrastructure project, the Vivekananda Road flyover, since 2009. There are 20-odd utilities at 32 places along the route from Girish Park to Posta.