The National Roads and Motorists' Association said the change had failed to slow drivers down and called for the government to commit the nearly $40 million revenue raised from fines to road safety initiatives.

Peter Khoury, the association's spokesman, said it was clear the effort to slow drivers down in the area was not working.

"If it was about pedestrian safety, clearly there's something wrong structurally. The NRMA's view on changing speed limits is that it has to be evidence based, it has to be backed up by data," Mr Khoury said.

"When you start to venture away from that approach, unfortunately, you lose transparency, you lose consistency. It's concerning that after all this time, you are seeing a 20-fold increase in fines."

Drivers caught by cameras in the city centre 40kmh speed zone - with fixed cameras on Barry Drive and Northbourne Avenue - have paid almost $40 million in fines since July 2021.

Nearly 4000 infringements a month have been detected by the cameras on Northbourne Avenue and Barry Drive in the first four months this year, around 20 times the average before the limit changed.

Mr Khoury said it was "alarming" that 4000 people a month were caught in the one zone.

The significant jump in the number of fines being issued also showed the way public trust in speed limits could easily be diminished, he said.

"The NRMA expressed concerns from the outset about the nature by which those changes had been introduced, the lack of education," Mr Khoury said.

"And it's critical if road safety is at the centre of decision making, then it's critical that the government views this data strategically.

"And we need to find a better approach to deliver the safety outcomes that were intended."

In the first four months of 2021, before the speed limit was reduced, the same cameras detected an average 207 infringements a month.

The ACT government had collected $38,370,053 in infringements from fines issued between July 1, 2021 and March 31, 2023.

"All revenue in relation to the collection of these infringements is transferred to the territory banking account," the government said.

But Mr Khoury said the revenue should be earmarked for road safety initiatives, which he said would negate the argument the cameras were purely to raise revenue.

He reiterated the NRMA's numerous calls for this to happen in the ACT.

"The NRMA successfully campaigned to have the hypothecation of all revenue from [speed] cameras back into road safety 11 years ago [in NSW]," he said.

"It's bewildering the same hasn't happened in the ACT."

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A spokesman for the ACT government said funds are not hypothecated to specific programs and contribute to overall government expenditure.

"The ACT government continues to make significant investments in road safety improvements across Canberra," the spokesman said.

"This includes hundreds of millions dollars of investment in major road safety upgrades like the Monaro Highway safety improvements, intersection safety upgrades, active travel upgrades focused on vulnerable road users, increased road maintenance program funding and new mobile device detection cameras."

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