Speed cameras on some of Canberra's busiest roadways have been out of action for as long as two years, as the ACT government struggles to make repairs across the network. 

Officials told a Legislative Assembly hearing on Thursday that the speed camera at the intersection of Ginninderra Drive and Coulter Drive in Florey had not operated since January 2012.

Another camera at the intersection of Marconi Crescent and Drakeford Drive in Kambah has been offline since February last year, while the camera at Hindmarsh Drive and Yamba Drive in Mawson has not operated since August last year. 

The camera on the Tuggeranong Parkway at Hindmarsh Drive last nabbed a speeding driver in February,  while the busy Barry Drive and Northbourne Avenue intersection camera has been down since March.

The revelations are embarrassing and expensive for the government, which collected more than $11.48 million in fines around the ACT in the year to March. 

Drivers will have also received fewer speeding fines from Canberra's mobile camera vans, with officials telling the budget estimates hearing that just two of the five vans are operational. 

More than 47,000 fines were issued to drivers on ACT roads in the year to March, with most from the 13 fixed and 13 red-light speed cameras. 

Attorney-General Simon Corbell defended the network and said sourcing replacement parts for older cameras was increasingly difficult. 

The information comes after a damning report by the ACT Auditor-General and just weeks before the government receives another study into speed cameras completed by the University of NSW's Transport and Road Safety Research group. 

"In 2013-14, the government allocated $1.55 million for the replacement of red light and mobile cameras as needed," Mr Corbell said. "This replacement program is expected to be completed by mid-2014. 

"If the further evaluation of the program, which is now under way, highlights priority sites where cameras could be used there is the option to relocate cameras to alternative locations." 

In March, the Auditor-General Maxine Cooper slammed the way speed cameras are used in the ACT and said there was no evidence the presence of cameras reduced speeding.

Her report found speed camera reliability remained poor, while escalating maintenance costs and too many rejected infringements were limiting their effectiveness.

Dr Cooper said the government was ‘‘unlikely to have the right number of speed cameras in the right places’’.

The government has previously said the UNSW report would be completed by mid-2014. 

Officials told the hearing that 85 per cent of operating cameras were collecting data on speeding drivers and 11 new cameras would soon be installed. 

Mr Corbell rejected suggestions from opposition transport spokesman Alistair Coe that the system had been operating without any strategy.

"It is easy to be wise in hindsight but the government takes its decisions based on the best available information, available to it at that time," he said.

"The speed camera network, as confirmed by the auditor-general, catches people who are speeding and it does so reliably and accurately.

"The auditor-general did not conclude the cameras were in the wrong locations … [but] that more work needed to be done to ascertain whether or not they were at the best locations, or if other locations should be considered," Mr Corbell said.