Traders in a Dorset town hosting the 2012 Olympic sailing events claim a £9m scheme to ease road congestion ahead of the Games may put them out of business.
The road works aim to help Weymouth cope with an increase in traffic when it hosts the events with Portland.
The first phase got under way earlier and is due to last until the end of the year. Hotel owner Loraine Godwin said the works could drive tourists away.
Dorset County Council said any unacceptable delays should be reported.
Five roundabouts are being replaced with "intelligent" traffic lights that communicate with each other.
Westham Roundabout, at the end of Abbotsbury Road, and Harbour Roundabout, near Asda, are first to see work start.
The Chickerell Road junction and the mini-roundabout on Rodwell Road will also be altered during the first phase, while gas works will cause Boot Hill to be made a one-way route.
Ms Godwin, who owns the Richmoor Hotel on Weymouth Esplanade, believes the works should be done at night and with double shifts.
"People are going to be going home and saying 'you should see the state of Weymouth'," she said.
"We could have people deciding to stay away from Weymouth for the next two years because of the work.
"They will just presume that this is going to be ongoing.
"We have people arriving who have told us it has taken them an hour and a half to get maybe half a mile, before [the works] even start properly."
A second phase will get under way in King Street early next year, lasting six to seven months.
Dorset County Council project manager David Diaz said he was aware of the "frustrations".
He said: "We've a major contractor doing the works for us - they will be starting early in the morning and working as late as possible.
"We understand the problems created by road works and restricting traffic but we will do what we can to keep it flowing.
"We have a very tight programme to deliver over the next 12 months.
"We will work the hours we need to work to get the scheme completed on time, or ahead of schedule if possible."
The town centre works are alongside the building of a controversial £87m relief road between Dorchester and Weymouth ahead of the Games.