Delays are being reported as two major slip roads to and from the A52 in Derby are closed from today.
Slip roads to and from the A52 on to Wyvern Way are closed from today, one for 13 weeks - the other for 13 months.
From today (June 3), motorists will not be able to access the A52 westbound stretch towards Derby until July 2020.
Diversion signs will be in place during the closures, which will allow new slip roads and a new bridge across the A52 to be built.
Derby City Council said the scheme will deliver benefits and it was doing all it could to minimise disruption.
This work is just one stage of the A52 Transport Improvement Scheme, which aims to reduce congestion and improve journey times.
On Brian Clough Way, a temporary speed restriction is in place towards the Pentagon roundabout.
Arriva, who operate bus services across Derby, tweeted that delays are expected on services 1, 1A and F1, adding: "We will endeavour to keep our services as reliable as possible but delays will be expected.
"Arriva apologises for any inconvenience caused."
Trentbarton, who also operate bus services in the area tweeted: "As expected this is causing a few delays to the Red Arrow, Spondon Flyer, and Ilkeston flyer, but also traffic would appear to be diverting away from the A52 causing delays to Indigo and I4 going into Derby."