The Highways England work will involve providing new yellow box markings on the roundabout to encourage a better flow of traffic through the roundabout from the A345, north and south.
The markings will be put in place over two nights and will require the closure of the A303 between Longbarrow roundabout and Solstice Park junction.
Highways England’s Area Manager, Rachel Nichols, said:
We have listened to concerns raised by the local community and drivers about issues at the roundabout and designed new road markings which should help to improve the flow of traffic.
The work has been scheduled to be undertaken overnight to cause the least possible disruption and we would like to thank drivers for their patience while we carry out the improvements.
Road closures will be overnight between 8pm and 6am, on Monday 12 September and Tuesday 13 September, and fully signed diversion routes will be in place as follows:
Countess roundabout to the Solstice Park junction: traffic will be directed to follow the A345 Countess Road southbound to then take London Road to re-join the A303 eastbound from the Solstice Park junction.
Longbarrow roundabout to Countess roundabout: traffic will be directed to take the A360 northbound to then take the B3086 northbound and take The Packway eastbound to then take the A345 Countess Road southbound to rejoin the A303 eastbound.
Solstice Park junction to Countess roundabout: traffic will be directed to follow Solstice Park Avenue westbound to then take London Road westbound and then to take the A345 Countess Road northbound to rejoin the A303 westbound.
Countess roundabout to Longbarrow roundabout: traffic to be directed to follow the A345 Countess Road northbound to then take The Packway westbound to then take the B3086 southbound to then take the A360 southbound to re-join the A303 westbound.
Members of the public should contact the Highways England customer contact centre on 0300 123 5000.
Journalists should contact the Highways England press office on 0844 693 1448 and use the menu to speak to the most appropriate press officer.