A road bridge or underpass will now be needed as part of long-awaited improvements to the worst bottleneck on the region's railway network.
Politicians and business leaders heard work on Ely North junction could be included in the government's next spending round, which runs from 2019 - 24.
A summit in the city, hosted by South West Norfolk MP Elizabeth Truss, heard studies looking at how the work might be carried out were now under way.
Meliha Duymaz, Network Rail's route managing director for Anglia, said the improvements were originally due to be carried out between 2009 - 14 but the scheme had been deferred.
She said the delay had given Network Rail the opportunity to review whether the scheme was the best way to improve the network for passengers and the freight industry.
Improvements at Ely North would enable more frequent services to run on the King's Lynn to London and Norwich to Cambridge lines, bringing an expected £1bn annual boost to the region's economy.
But Bob Menzies, director of strategy and development at Cambridgeshire County Council, said there were three level crossings along half a mile of road at Queen Adelaide, where lines leave the junction.
'If you increase the amount of trains, you increase the amount of time these crossings are going to be shut,' he said.
Mr Menzies said currently 4,800 vehicles a day used the stretch of road through Queen Adelaide.
But 3,000 new houses are due to be built around Ely, which will increase traffic through the village to an estimated 8,000 vehicles a day.
Mr Menzies said an underpass or bridge would be needed as part of the junction scheme.
'What we need to do now is progress road and rail schemes in tandem so we can have a workable scheme by next year,' he added. 'We need to do our job as professionals so you can do your job as politicians and get the thing funded.'
All major rail schemes are now considered on a case by case basis. A business case is being drawn up setting out the potential benefits from Ely North which will be submitted to government in April.
Mid Norfolk MP George Freeman said the work would unlock growth and clear the 'blocked artery' preventing half-hourly trains between Cambridge and King's Lynn and Norwich and Cambridge.
'If we want people to be part of the modern East Anglia, they've got to be connected so they can get to the opportunities,' he said.
James Palmer, mayor of Cambridgeshire and Peterborough, said Cambridge's economy would begin falling behind other world-leading cities without the investment.
The meeting also heard design work to extend platforms at Littleport and Waterbeach was now under way.
Ms Duymaz said once completed, the work would enable eight-carriage trains to run between King's Lynn and Cambridge, easing over-crowding.
The trains were originally due to enter service this year. Ms Duymaz said the improvements would now be completed 'as early as possible in 2019'.
North West Norfolk MP Sir Henry Bellingham said: 'It's disappointing because the promise was made and it's not been kept.' He added services between Lynn and London were 'almost Third World', with overcrowding and trains cancelled or running late.
'People are getting very angry,' he added. 'People are saying to me back in 1950 we had eight-carriage trains, up until 1985, so why can't we do it now.'
Mr Freeman said he would be amazed if there was a route with worse overcrowding than the Fenline.
Keith Jipps, infrastructure director for the Great Northern route, said it did not even feature in the top 10 most-crowded lines.
Sir Henry asked why conductors were being reduced on trains. Mr Jipps said the company was spreading its resources where they could be most effective.
Sir Henry said cutting refreshment trolleys between Lynn and London 10 years ago had been 'a hugely retrograde step'.
He added: 'It must be one of the few railways in Europe where there aren't refreshments on their train over such a long distance.'
Mr Jipp said: 'We have struggled to find anyone who'd be interested in providing a quality service on the train.'
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