Infrastructure Secretary Keith Brown has admitted “one or two” average speed cameras on the A9 are not yet operational.
But he stressed that the situation did not “affect the viability of the entire system” which was monitoring the Inverness to Perth road in a bid to reduce accidents.
Mr Brown hit out at Highland MP Danny Alexander who he claimed had been “playing politics from day one” by opposing to the £2.5million scheme, which comprises of about 100 cameras.
But the “silly allegation” was dismissed by the Liberal Democrat politician who said his number one priority was to listen to the concerns of local people.
The admission that not all the cameras were working comes days after Mike Burns of the A9 Average Speed Cameras are not the Answer campaign group said he had been told by an engineer that not all the devices had power.
The A9 Safety Group, which is publishing speeding ticket details next month, has revealed not all locations along the route are configured to be “live” at the same time.
Instead, police can choose which enforcement sections they wish to activate, based on driver behaviour.
Mr Brown said one of two cameras were still waiting for way leaves – landowner permission – but the system was “live and connected”.
“So people should not take the idea that the cameras are not on because they are apart from one or two exceptions,” he added.
“But it does not affect the viability of the entire system.”
Mr Brown said it was “preposterous” that Mr Alexander was claiming the scheme had turned local roads along the trunk route into rat runs as drivers tried to dodge the devices.
“In fact there has been a 5% increase in usage on the A9 and we get an awful lot of positive feedback now from people about their experience of the cameras,” he added.
“We have responded to safety concerns, it was the right decision done for the right reasons and Danny Alexander is playing politics and has been since day one.”
Mr Alexander said thousands of people have contacted him to voice opposition to the cameras, before and after they were activated.
“And now constituents in communities on the A9 corridor are telling me they are seeing traffic trying to avoid the yellow vultures,” he added.
“Far from a ‘preposterous’ assertion, Mr Brown has written me a letter today saying he will investigate the use of B-roads as rat runs.”