The ACT Government has advised motorists of a speed limit reduction on a section of William Hovell Drive – one day after it actually came into place.

Roads ACT director Tony Gill has conceded it could have done better to communicate the permanent reduction in the speed limit from 90km/h to 80km/h on William Hovell Drive between Coppins crossing Road and 500 metres east of Bindubi Street.

But he denies it had anything to do with trying to avoid previous controversy over the speed limit in the Gungahlin Drive Extension.

The new speed limit on William Hovell Drive actually came into place on Wednesday to improve safety on the road.

Four local politicians also failed to mention the speed limit reduction when they announced a range of road safety projects earlier this month.

Chair of the ACT Black Spots Committee and Federal Member for Fraser Andrew Leigh, Federal Member for Canberra Gai Brodtmann, Senator for the ACT Kate Lundy and ACT Chief Minister and Minister for Territory and Municipal Services, Katy Gallagher, made a joint statement on April 8 in which they mentioned "upgrading works" at the intersection of William Hovell Drive/Bindubi Street, Belconnen but failed to mention the speed limit reduction.

Mr Gill said the reduced speed limit was a result of road safety concerns raised as part of the Nation Building Black Spot Program.

"There has been a total of 11 casualty crashes at the intersections of William Hovell Drive/Coppins Crossing Road and the intersection of William Hovell Drive/Bindubi Street in the last five years," he said.

"A report completed in August 2011, which assessed the safety of William Hovell Drive, recommended that the speed limit be reduced from 90km/h to 80km/h.

"William Hovell Drive was the only road in the ACT with traffic lights that had a speed limit of higher than 80km/h.

"By reducing the speed limit to 80km/h we are mitigating the risk of accidents at the intersections of William Hovell Drive/Coppins Crossing Road and William Hovell Drive/Bindubi Street.

"This speed reduction is part of road improvements including traffic signal enhancements and intersection upgrade works at the Bindubi Street intersection.

"The 80 km/h speed is consistent with speed limits on other arterial roads with traffic light intersections in the ACT and in other jurisdictions across Australia.

"Motorists are urged to adhere to the new speed limit which is signposted," Mr Gill said.

Variable message signs have been erected to advise motorists of the reduced speed limit.

For up-to-date information on road closures please call Canberra Connect on 13 22 81.