Main construction has started on the duplication of William Hovell Drive, with the ACT and federal governments jointly funding the $107.25 million road upgrade.

The project will duplicate 4.5 kilometres of William Hovell Drive between John Gorton Drive and Drake-Brockman Drive, creating two lanes in each direction.

The ACT Government says the upgrade is aimed at reducing congestion and improving safety for the more than 20,000 vehicles using the corridor each day.

Preparatory works, including surveying, dilapidation assessments and site compound establishment, were completed over the past month ahead of the main construction phase.

The project also includes a new signalised intersection, a shared walking and cycling path, improved access to the underpass and Old Weetangera Cemetery, and wildlife crossings.

The duplication is being delivered alongside the new Molonglo River bridge project, which is expected to open later this year and is intended to support future growth in Belconnen and the Molonglo Valley.

Population modelling cited by the Government projects Belconnen could exceed 185,000 residents by 2065, while the Molonglo Valley could accommodate another 79,000 people.

To allow construction to proceed safely, overnight road closures will be in place on William Hovell Drive between Drake-Brockman Drive and John Gorton Drive from 8pm to 6am between May 25 and May 30, weather permitting.

Construction is expected to take about three years.