The A360 north of Salisbury will be closed from today until mid-July to allow high-power electrical cables to be installed.
The A303 Stonehenge project needs an electricity supply for construction and for the tunnel once built.
Scottish and Southern Electricity Networks (SSEN), working on behalf of National Highways, will carry out work along the A360 to provide power and install high-voltage cabling.
Between today and July this year, a section of the A360 will be temporarily closed to the south of the A303 between Longbarrow roundabout and The Avenue roundabout to allow the work to be done as safely and as quickly as possible.
During the closure, traffic will be diverted via the A345 and sections of the A303 and A36. Road signs will be in place to direct traffic to alternative routes.
Camp Hill and the Stoford to Woodford Middle road, which crosses the A360, will remain open throughout the works. Temporary weight restrictions will be in place on these roads.
David Bullock, National Highways’ Project Director for the A303 Stonehenge scheme, said: “We need to carry out the work now to ensure our programme timescales and we want to give local communities as much notice as possible.
“We appreciate that roadworks and road closures can be frustrating and we’d like to thank motorists, local residents and businesses in advance for their patience.
“Without the full closure, the work would take a lot longer to complete, and we’re making every effort to ensure that the impact on drivers and local communities is kept to an absolute minimum.