The historic Trowse Swing Bridge on the outskirts of Norwich could be replaced by 2024 under plans set out by Network Rail in its blueprint to speed up and increase the frequency of trains heading out of the city.

The historic Trowse Swing Bridge on the outskirts of Norwich could be replaced by 2024 under plans set out by Network Rail in its blueprint to speed up and increase the frequency of trains heading in and out of the city.

The single-track line to Norwich station has been highlighted as a major obstacle to increasing the frequency of services, and the rail infrastructure firm has included a project for the bridge, which could cost up to £75m, in its plans.

By law Network Rail has to open its bridges on demand to allow free passage to vessels, so if fixed bridge was constructed, the law would have to be changed.

The Trowse bridge has not been working since May 2013, and before that was beset with failures, only working some of the time.

A Broads Authority has been urging Network Rail to sort out the problems, and said it wanted to work with the firm to resolve the issues, so groups like the Brundall Yacht Club and the Sea Scouts, who would like to use it regularly, were able to.

She said: 'During high season we get seven to eight requests from visitors a week but no longer get many requests from local groups or individuals, but only because they are aware of the ongoing issues with the bridge.'

Network Rail's plan looks at how the Government will cope with expected spiralling demand for rail travel over the coming decade.

Studies show that the Great Eastern Main Line into Liverpool Street from stations in Suffolk and Norfolk could see passenger numbers grow by 32pc, while the amount of freight transported by rail could grow an average 2.9pc each year over the next three decades.

Government cash has not yet been found for the work and the document will form part of its decisions as rail leaders make the case for a bigger slice of the sought after rail cash.

Its publication comes as the business case for an upgrade to the line has landed on the Chancellor and Transport secretary's desks. The Great Eastern Rail Taskforce report claims that a £467m investment in the line could reap a £4.5bn economic boost to the region's economy.

It warned that without investment, growth would be stifled, our services would be run into the ground and passengers would be 'condemned' to 'at least another decade of misery'.

Richard Schofield, Network Rail route managing director, said: 'Over the last twenty years the industry has been able to massively increase the frequency of services, but we're fast approaching the point where there simply isn't any more space for more trains on the busiest parts of the network. We have to look at ways of increasing the capacity of our network further, including new technology to allow more trains to run on existing tracks, and perhaps building new tracks in key locations.'

Mark Pendlington, chairman of New Anglia LEP, said: 'Network Rail rightly identifies that urgent work is needed on the infrastructure of the Great Eastern Main Line - including upgrading the track, signalling and over-head line equipment - to increase line speeds and capacity and ensure we can get from London to Norwich in 90 minutes, Ipswich in 60 and Colchester in 40. This is exactly what we have outlined in our report to Government and why we have asked for £476m investment to make these improvements.'

Consultation on the draft Anglia Route Study is open until February 3 2015.

Once complete, the final plan will be published next summer and will be used by the Department for Transport to plan funding period from 2019 to 2024.

To comment on the study please email AngliaRouteStudy@networkrail.co.uk