After months of planning, Monday is the moment of truth for the people who run East Anglia's rail network - because Ipswich tunnel is closing.
The Victorian structure is having to be dragged, kicking and screaming, into the 21st century.
This is so massive freight containers can be transported between the Port of Felixstowe and the rest of the UK.
But it is likely to hit passengers on the Norwich to London line which passes through Ipswich and Colchester.
Passengers are now having take coaches for the mid-section of their journeys to and from the capital.
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It's a pain it has to happen, and it will be such an inconvenience
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On Sunday, commuter Mark Cullen, who lives in London and works in Norwich, said the nuisance factor is going to be so high he is looking at serious measures to save himself the 30 to 45 minutes added to each journey.
"It's a pain it has to happen, and it will be such an inconvenience. I've actually started looking for a flat to rent in Norwich for the next two or three months because it's going to add so much to journey each way," he said.
Kevin Rider, from Ipswich, said although a lot of planning has gone into the coach link and car parking, he is unsure that other passengers are going to know what to do.
"I normally travel into London every day," he said.
Essential work
"But because we knew there were going to be a lot of problems in the first week of travel, I've taken a week's holiday to avoid all the disruption and chaos.
"A lot of thought's been made about the trip from Ipswich to Manningtree, but I don't think there's been a lot of consideration to the fact they'll have 450 to 500 people getting off the train coming back into Manningtree at night."
One Anglia, the Strategic Rail Authority and Network Rail have been working together for the past year or so on how to ease the travelling public through this essential work.
Jonathan Denby, a spokesman for One, said: "It's been very well planned, based on previous blockades in other parts of the country, allied with how many regular passengers there are on our route.
Cambridge option
"It should be OK, but clearly in the first week, we'll look at it, we'll review it, if there are any pinch points, we'll seek to address them."
For those who live in Norwich, and cannot face the disruption at Ipswich and Manningtree, Mr Denby said there is another way.
"We've put in two direct trains on weekdays between Norwich and London via Cambridge which don't stop anywhere on route," he said.
"We've tried to give passengers as many choices as we can, especially for those who really don't want to go on a bus."
The work Is expected to be complete by 5 September.