A community the size of Haverhill would need to be built around the north of Ipswich to make it economically viable to construct a new northern bypass, according to the long awaited report into the proposed new road.
And that is not the only hurdle.
More than two thirds of the residents who took part in the consultation at the end of last year were opposed to any new road, with only 26% of respondents in favour.
There was a clear geographical split - almost all those supporting the new road plans were from Ipswich itself while the majority of those opposed to it were from the communities to the north of the town.
While the consultation says that the cost would be between £342m and £385m, that is a figure if it was built today, with the actual cost between £500m and £560m when it would be constructed, if the project continues.
The new road would require between 15,000 homes to be built to make the cost viable - and opponents of the new road believe the total cost could be much higher and require many more homes.
Those 15,000 homes is understood to be on top of existing housing allocations in the districts' local plans.
The report does say the inner route would provide a reasonable return if the new homes are built. The middle and outer routes could not provide the funding to make them viable and seem very unlikely to be progressed further.
Suffolk County Council now has to decide whether to go ahead with more detailed plans for the road. Public sector leaders have already spent £550,000 reaching this stage and a more detailed study coming up with an exact route and working out detailed costings would be much more expensive.
The county's cabinet is expected to discuss this at its meeting at the end of next month - but before then it is expected to hear the views of East Suffolk Council and Mid Suffolk Council. Both are known to have many councillors opposed to the new road - an opposition shared by their MPs Dr Dan Poulter (through whose constituency most of the road would be built) and Dr Therese Coffey.
Suffolk County Council leader Matthew Hicks, said: "I am pleased that Suffolk County Council has delivered on its commitment to complete phase one of the Ipswich Northern Route project.
"This phase of the process was commissioned and funded by Suffolk Public Sector Leaders, so it is entirely right that the SOBC be returned to them so that together, we can consider the findings, and decide whether this project should proceed to phase 2.
"Whilst Suffolk County Council, as the transport authority, has the responsibility for submission of any transport scheme to the Department for Transport, we have throughout this project emphasised the need for a Suffolk wide collaborative approach if this project is to enjoy any realistic chance of success.
"I look forward to receiving the views of my fellow leaders in due course."
Central Suffolk and North Ipswich MP Dr Poulter has been a leading critic of the proposals and said he was very dubious about the cost of building the road: "They seem to have put a very low value on the land they would need to buy - I am not sure that is at all realistic," he said.
However the road has its supporters. Ipswich council leader David Ellesmere said: "The Strategic Outline Business Case shows that not only is a Northern Bypass good value for money, it would be much cheaper to construct and require many fewer houses to be built than some of the figures bandied around by its detractors.
"I am pleased that the business case identifies the inner route - Ipswich Borough Council's preferred option - as the one with the highest cost-benefit and the highest level of public support. The past few weeks have shown the continuing damage to Ipswich's economy whenever the Orwell Bridge closes.
"We've had enough of delays on our roads and delays by Suffolk County Council. They should commit immediately to submitting a full business case for the bypass to the Government."
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