The $1.34 billion widening of the Tullamarine Freeway and Citylink will begin after Monday night's evening traffic peak.

The first stage of construction will take place between Bulla Road and Bell Street, with speed limits reduced to 80 km/h and lane widths reduced in that section. It is expected the number of lanes available will remain the same during peak traffic periods.

Extra lanes will be added to the Tullamarine Freeway and CityLink between Melbourne Airport and the Burnley and Domain tunnels, which will increase the capacity of the road by 30 per cent. The whole project is expected to be completed by the end of 2018.

Transurban CEO Scott Charlton said the company would work with VicRoads using smart technology to try and keep speeds at 100 km/h in off-peak times.