Birmingham's city centre Queensway tunnels, notorious for traffic chaos, could be lengthened under plans being considered by Labour councillors.
A party think tank is proposing connecting the St Chad's and Queensway tunnels to make Great Charles Street a " pedestrianfriendly boulevard".
The scheme, involving building a new tunnel, would reconnect the central business district to the Jewellery Quarter and make it easier for people to move between the two areas, according to Labour.
The idea, which was first floated in the 1980s, is contained in a policy discussion document published today which sets out the views of the city council's Labour opposition group on the growth of Birmingham up to 2015.
But the proposal was criticised as "barmy" by the council's Tory cabinet member for transportation, Len Gregory.
Coun Gregory (Billesley) said the tunnels, which have only two lanes each way, were accident blackspots and often the cause of severe delays during rush hours.
Police closed the Queensway tunnel on Wednesday morning this week in order to tow away a broken down car, resulting in a three-mile tailback to the M6.
Coun Gregory added: "This would just make life much more difficult in the event of an accident.
"This typifies Labour's approach to transportation. It would cost many millions of pounds and bring no benefit."
The cost of building a new tunnel between Newhall Street and Livery Street has not been estimated by Labour.
But the party believes the project could be financed by selling land off Great Charles Street that was once earmarked for a new coach station.
The proposal has been singled out by Labour as an example of the way Birmingham needs to "think big" on regeneration.
Labour has accused the council's Tory-Liberal Democrat leadership of being too timid and dithering over delivering large projects.
Ian Ward, deputy leader of the Labour group, defended the decision not to cost the scheme.
Coun Ward (Shard End) added: "This is not a manifesto. It is a discussion document and we want to know what people think about our ideas for Birmingham.
"The intention would be to use the capital raised by the sale of the former coach station site to pay for the construction of a new tunnel.
"We think that is the right way to improve the connectivity between the city centre and the Jewellery Quarter."
Birmingham Chamber of Commerce and Industry reacted with caution to the idea.
A BCCI spokesman said businesses would fully support the pedestrianisation of Great Charles Street, but the impact of an additional tunnel would have to be examined carefully.
"Traffic in the city centre is already on a knife-edge. You only have to have a bumper drop off a car and there are miles of tailbacks," the spokesman added.
Labour is also promising: n to press ahead with the extension of the metro tram system through the city centre n plans to build a split-site library would be abolished in favour of a one-site option at Eastside n the planned redevelopment of New Street Station would be expanded to take in a larger site
The document claims that Birmingham's reputation for regeneration is at risk and that the city has been overtaken by Bristol, Leeds and Manchester in terms of growth.
Labour says: "We need to imagine Birmingham in ten years time. We need to think about what it should look and feel like.
"By 2015, Birmingham should have a greater sense of ambition and purpose, but also confidence.
"Birmingham, its politicians, residents and business community must continue to think big, be ambitious and act courageously in shaping the agenda and delivering the future."
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