Birmingham’s St Chad’s Tunnel could be filled in and the neighbouring Queensway overhauled in an ambitious £85 million scheme being considered by the council’s transport department.

The four-lane tunnel, running under Snow Hill near St Chad’s Cathedral could be raised to a street level dual carriageway, opening up land for development, the Birmingham Post can reveal.

The plan will also break the “concrete collar” to the north of the city centre, opening up pedestrian links to the Jewellery and Gun Quarters and creating a new plaza or attractive boulevard.

Meanwhile, the Queensway Tunnel, under Paradise Circus, would be refurbished and extended along the weaving section of Great Charles Street Queensway to open up at St Chad’s. Great Charles Street would then also be opened up for development above ground. The plan is the most extensive of three options looked at by transport consultants Atkins in a feasibility study handed to the council last month.

Option zero is the low cost scheme to maintain the tunnels in their present form, but with a clean-up and repair work to the ventilation system. But the plan would leave poor concrete in St Chad’s tunnels, which would need heavy maintenance work in future.

Option one would link the two tunnels to create a long single tunnel from the end of the Lancaster Circus flyover to Suffolk Street, with an estimated price tag of £64 million. A key risk here would be the knock-on effect of an accident in the tunnel requiring evacuation and diversions.

The risks identified for the £85 million option two were cost, the extent of the works, impact during construction and the fact it would mean remodelling St Chad’s junction, which was only created in 2007.

The study estimated that construction could take up to five years if traffic is to be allowed and managed through the roadworks, or as little as two years if vehicles are completely excluded from the construction area.