New speed limits have come into effect for Civic, Belconnen and Tuggeranong town centres, slowing drivers to 40km/hr.
The new limits follow a trial of slashed speed zones in Gungahlin and Woden in 2011, as well as two months of community consultation last year.
The new speed limits are in place along the upper half of London Circuit, Cooyong Street and Marcus Clarke Street in Civic.
Benjamin Way, Chan Street and Lathlain Street are affected in Belconnen, and the central retail area around Athllon Drive, Pitman and Anketell streets are affected in Tuggeranong.
The new limits will be in place 24 hours a day, seven days a week, Territory and Municipal Services Minister Shane Rattenbury said.
“These are town centre areas with high pedestrian movement and a substantial level of retail and commercial development,” he said in a statement.
“Implementing safer speed limits in areas with high pedestrian and cyclist activity is in line with national and ACT road safety strategies and is a proven road safety measure.”
Mr Rattenbury said research had found that reduced speed limits in urban areas lowered the risk of collisions, as well as the severity of collisions.
“A 10 km/h decrease in speed from 50 km/h to 40 km/h can reduce the risk of death for pedestrians and cyclists involved in collisions by over 50 per cent,” he said.
The government announced the reduced speeds in April, but at that time said only they would be introduced "midyear". It is also installing traffic calming measures: speed cushions and small speed humps.
The combined cost of the measures is $170,000.
The government will evaluate the changes after six months.