A Dorset council is trying to tackle the severe congestion caused by its preparations for the Olympic games.
The £9m scheme to improve traffic in Weymouth, ahead of the town hosting the 2012 sailing events with nearby Portland, has caused major disruption.
Some motorists were ignoring diversion routes and using residential roads as rat-runs, creating further congestion.
Dorset County Council has now altered signalling on the route which it hopes will cut motorists' queuing time.
It said some roads in the town had seen an increase of traffic of 75% by drivers seeking short-cuts.
The Weymouth Transport Package, which began Monday 7 June, involves the installation of traffic lights at five roundabouts in the town.
Project manager David Diaz said most drivers were now using the suggested diversion of Lanehouse Rocks Road to Chickerell Road, instead of ignoring an access only turn into residential Lynch Road.
He said: "We have changed the signals on the Lynch Road junction at Fiveways to keep traffic waiting longer to try and dissuade people from rat-running along the road."
John Sapsford, a local taxi firm manager, was involved in suggesting some of the diversionary routes to use during the works.
He said: "People have to understand that they are going have to live with the disruption in order to benefit from the long-term improvements."