And the ACT government has defended a plan to install traffic calming devices in Canberra's CBD to slow drivers down.

Road users gave a mixed reaction on Wednesday to the plan to drop speed limits in the busiest areas of the town centres to 40km/h by mid-year.

The upper half of London Circuit, Cooyong Street and Marcus Clarke Street will become 40km/h zones.

In Belconnen Benjamin Way, Chan Street and Lathlain Street are among the roads that will have their speed limits reduced.

In Tuggeranong, the central retail area around Athllon Drive, Pitman and Anketell streets will be affected.

"Speed cushions", small speed humps, will also be installed throughout the Belconnen and Tuggeranong town centres and on Akuna and Allara streets in Civic.

Watson resident Dipti Patel, who regularly walks through Civic, said she thought the 40km/h zones would make the area safer for pedestrians.

"This area is very busy and people like to walk freely through here," she said. "I think 60km/h is too fast."

James Moore, also of Watson, said he regularly cycled to work and was supportive of the 40km/h zones, although the existing 60km/h zones did not worry him.

"The speed of the traffic through here doesn't really bother me, but I still think [40 km/h] is a good idea," he said.

"It's not going to be a big imposition because there's no real time saved by going that little bit faster."

But Wanniassa resident Peter Haynes said 40km/h zones would have little effect on drivers through Civic as they would not change the habits of speeding motorists.

"You don't get to 60 much through Civic anyway and there's no way in Tuggeranong you can do 60 because of all the speed humps," he said.

"It seems like change for changes sake.

"It's not going to change the habits of people who are just going to speed anyway."

Canberra Liberals urban services spokesman Alistair Coe said he doubted that "many motorists are driving dangerously at high speeds in these areas at the moment".

The Deputy Opposition Leader said 40km/h signs could also be easily missed by motorists in Civic, where there was already a lot of existing road signage.

"The installation of speed cushions may also cause drivers to act erratically and be more focused on their approach to the cushion, rather than concentrating on nearby pedestrians and cyclists," Mr Coe said.

But TAMS Minister Shane Rattenbury said the traffic-calming devices were necessary as a form of "passive enforcement" of the new speed limits.

"We obviously don't have the capacity to have a speed van there or a police officer there 24/7, so the traffic-calming measures are part of that ongoing passive enforcement of the speed limits," he said.

"They're designed to just provide that constant reminder to people of the necessity to reduce their speed."