Work on a £9m scheme to relieve traffic congestion in Weymouth ahead of the 2012 Olympic Games is due to get under way on Monday.
The scheme aims to help the town cope with an increase in traffic when it hosts the sailing events with Portland.
Five roundabouts are being replaced with "intelligent" traffic lights that communicate with each other.
Work starts on Westham Roundabout, at the end of Abbotsbury Road, and Harbour Roundabout, near Asda, on Monday.
The Chickerell Road junction and the mini-roundabout on Rodwell Road will also be altered during the first phase of works, the council said.
All the junctions being replaced currently suffer from severe congestion, with public transport particularly badly hit.
But the works themselves will cause disruption.
Dorset County Council project manager, David Diaz, said: "We'd ask drivers to be patient with us, but if they experience unacceptable delays we'd ask them to contact us so that we can adjust our traffic management where appropriate.
"This work will cause disruption but when these schemes are finished, residents' will have a modern transport network and substantially more choice of how to travel around the town."
Southern Gas Network will also be working on Rodwell Road from Monday, causing Boot Hill to be made a one-way route during the works.
The town centre works are alongside the building of a controversial £87m relief road between Dorchester and Weymouth ahead of the 2012 Olympics.
The council is also working to improve Weymouth's bus stops and is constructing three new cycleways and completing "an accelerated road maintenance schedule" in the borough.
The towns of Weymouth and Portland will play host to 400 international sailors during the 2012 Olympic and Paralympic Games.