A £7m upgrade of the Windsor and Eton relief road and improvements to the Clarence Road roundabout in preparation for the 2012 Olympics has begun.
The start date has been timed to avoid the high traffic period of Royal Ascot, and will carry on until March 2011.
Most work will take place at night, but during the first few weeks some daytime working will be necessary to lay electricity cables.
The off-peak work will affect only one lane in one direction at any one time.
The Windsor and Eton relief road is the busiest in Berkshire, according to the Royal Borough of Windsor and Maidenhead, carrying up to 22 million vehicles a year.
It will be a main route for spectators at Dorney Lake during the 2012 Olympics.
The Clarence Road roundabout will be also be redesigned to improve the flow of traffic through this key junction and all the work will be carried out at night.
Eton Wick residents will gain an early benefit with a barrier being installed in the first phase of works to reduce noise.
The council says strict noise levels have been set to protect residents.