Average speed cameras have been put in place at a number of sites between Perth and Inverness as part of a £2.5 million project.
Although the system is still being tested ahead of going live in October, motorists have reported a significant change in driver behaviour.
One campaigner said average speeds in camera zones were as low as 32 mph, describing it as "a complete farce".
David Thomson said: "Lorry drivers are now sitting at less than 40 mph because of the cameras, causing complete chaos.
"Whenever there is a gap, motorists are taking even more chances than before. I dread to think what it will be like once all the cameras are installed."
Meanwhile, other drivers have reported queues of between 40 and 50 vehicles, as well as an increase in dangerous overtaking manoeuvres.
Work to install the average speed cameras began last month.
The A9 is regarded as one of the most dangerous roads in Britain, with the rate of fatal and serious road accidents on the Perth-to-Inverness stretch of road much higher than the national average.
The installation of the cameras comes as the Scottish Government moves forward with its plan to make the route a dual carriageway.
The £3 billion project involves the upgrade of 80 miles of single carriageway along the A9 between Perth and Inverness by 2025.
The founder of the A9 Average Speed Cameras Are Not The Answer campaign, Mike Burns, called for a public inquiry into the project.
He said: "Drivers are now reporting a rise in observed risky overtaking manoeuvres, an average speed which is so low as to render the A9 a no-go zone for many drivers.
"This will cause a significant impact on the Highland economy. Transport Scotland and the A9 Safety Group must be subject to a public inquiry on this fiasco and for adopting a scheme which could be construed as negligent by creating conditions which are creating worse driver behaviour."
A Transport Scotland spokesman said: "The A9 Safety Group is clear that average speed cameras are effective in saving lives. Claims that speed is not an issue on the A9 have no foundation in fact. Of the offences recorded by Police Scotland and the Safety Camera partnerships last year, more than 95 per cent were speed-related.
"The comments in terms of the role speed plays in accidents have been misrepresented.
"It is unfortunate the campaign group has rejected the recent meeting offered to them by the chairman of the A9 Safety Group.
"This would have allowed us to address the lack of understanding of the work that is being carried out and explain the role the cameras have in supporting safety on the A9."
Last week it was revealed speeding motorists could lose their licences in just a single journey on the roads as they would be fined £100 and given three penalty points each time they were caught by a camera.
Anyone caught breaking the limit - 60mph for cars and 50mph for lorries - in just four of the eight zones would clock up 12 penalty points, enough for a ban.
Highland Liberal Democrat MP Danny Alexander has vowed to keep up his efforts to get SNP ministers to scrap the scheme.