Highways England recently completed £3.27m of improvements on the roundabout, which is located approximately half a mile to the west of the Saltash Tunnel.
Feedback from drivers indicated that slight alterations to the finished project might help their journeys.
Alexis Field, team leader for Highways England in Devon and Cornwall said: "We take very seriously any concerns raised with us and while the road markings passed our safety checks, drivers told us that changes might help them navigate the roundabout.
"This coupled with our wider review of the roundabout’s operation lead us to decide to alter the markings.
"Significant works such as this often require some fine tuning and we hope to have the alterations completed by the end of September."
On the southbound approach of the A388, Callington Road, traffic destined for Saltash will be directed to the right hand lane, and the road markings on the roundabout amended to guide drivers through.
On the westbound exit on to the A38, the markings will be altered to provide more guidance for merging traffic.
Work at Carkeel Roundabout included widening the westbound approach from two to three lanes and widening the westbound exit to allow for a two lane exit.
A pedestrian footbridge on the A38 eastern arm was also installed.
