Cameras clocked more than 5000 motorists driving above the 40-kilometre speed limit through the city this week.
Drivers failed to adhere to the changed limit in the 48 hours after it was adjusted on Barry Drive and Northbourne Avenue in the city.
As part of a staged approach to the extension of speed limits, drivers will have a grace period where fines will not be issued.
From July 5, drivers face fines of more than $400 and the loss of three demerit points after the ACT government expanded the 40km-per-hour zones in the city in an effort to make roads safer for pedestrians, cyclists and public transport users.
Minister for Transport Chris Steel said the lower speed limit reflected the changed function of roads in the CBD and Braddon areas.
"The risk of death for a vulnerable road user drops from approximately 80 per cent when a vehicle is travelling at 50 kilometres per hour to 50 per cent when the vehicle is travelling at 40 kilometres per hour," he said.
"This makes a huge difference to someone's chances of coming home safely."
Minister of Business Tara Cheyne said the education period for drivers was coming to an end.
"The sheer number of motorists speeding in such a high-density area is concerning.
"The 40-kilometre-per-hour zones were introduced to create a safer environment for everyone using the roads. And it seems the message hasn't sunk in.
"Motorists caught speeding by between 15 and 30 kilometre per hour can face fines of over $438 and three demerit points. This means that some motorists will lose their licence if they don't change their behaviour."
