A city centre bridge, which has been a traffic bottleneck for a decade, is to be strengthened at a cost of £6 million.

The work will allow George Square to be closed to traffic for Commonwealth Games crowds and other major events.

In 2001 a strength test was carried out on Cathedral Street bridge which resulted in it being closed to traffic.

In November that year it was decided to re-open one lane of the structure and impose a 17 tonne weight restriction.

It had been hoped strengthening work would be carried out and that the traffic restrictions would be in place for only 18 months.

However a lengthy wrangle erupted between Network Rail and the city council over who owned the bridge and the restrictions remained in place.

The row was resolved in 2006 when it was agreed Network Rail, which owns and operates more than 40,000 rail bridges, viaducts and tunnels across Britain, was the legal owner.

However nothing was done to strengthen the structure which was built in 1877 and carries Cathedral Street over the railway lines that run in and out of Queen Street Station.

While Network Rail owns the bridge, and is legally obliged to ensure it can carry a certain weight of traffic, it is not obliged to bring it up to the standard the city council insists on for a busy road.

On Friday, councillors will be told the two organisations have agreed in principal that Network Rail will pay around £4.3m of the strengthening bill and the council £1.7m.

An unusual feature of the bridge is that it also provides support to the end of the roof of Queen Street Station, which is an A-listed building. Historic Scotland includes the bridge in that listing.

Jim Coleman, the city council's land and environment spokesman, said: "The bridge completes a major east-west route through the city centre.

"The closure of the north footway, removal of all the bus stops on the bridge and repositoning of the south footway onto the carriageway has been, and remains, a major inconvenience to shoppers, students and all the other pedestrians who use the bridge.

"The unrestricted use of the structure by traffic would allow Cathedral Street to be used as an alternative route and make the closure of George Square to vehicles a possibility.

"This in turn allows the Square to be used as a traffic free venue for Commonwealth Games crowds and other major events in the future.

"Working without the bridge for so many years has pushed a lot of traffic through Nelson Mandela Place and George Square, which is far from ideal.

"George Square is one of our most important locations for events but it has been constrained by the traffic situation.

"Once the bridge is back in use, we should have much more scope to look at removing traffic from around the square.

"The work will mean public transport can be fully reinstated to the Cathedral Street bridge, bus stops reopened and the bridge will take its place as an elegant structure within the proposed new Buchanan Galleries and Queen Street Station developments.

"The full benefits of an efficient road network cannot be realised if the weight and lane restrictions remain on the bridge.

"Without investment, the structure would deteriorate further and eventually we would have been looking at a complete closure – even to pedestrians.

"The current restrictions are nearly 10 years old and are a blot on the city landscape.

"The council will now provide £1.73m of capital funding to ensure Network Rail's bridge is not only made safe for the future but strengthened to a degree where it can be brought back into the road network."

The work is planned to start in 2013/14 and will involve strengthening the main truss girders, overlaying the existing metal deck with a reinforced concrete one and repainting the complete structure.

This will allow reinstatement of three lanes of traffic and allow 40 tonne vehicles to use the bridge.

A Network Rail spokesman said: "We are working with Glasgow City Council to develop plans to strengthen and refurbish the bridge.

"Network Rail is committed to delivering any enhancement of the infrastructure with the minimum of disruption to services."