Westminster's Scottish Affairs Committee said the proposals showed "a lack of planning''.
A9 Speed Cameras Switched On
Average speed cameras on one of Scotland's most notorious roads will be switched on today as part of a plan to improve safety and save lives.
Construction work on the new system for the A9 between Perth and Inverness began in May and it is now set to become operational.
In addition, a higher speed limit for HGVs on the route will also come into force today, with a view to reducing driver frustration caused by slow vehicles on the busy road.
The increase from 40mph to 50mph is being trialled under a pilot project.
It is hoped both measures will help reduce the accident rate on the A9, which is the main road between central Scotland and the Highlands.
It is commonly regarded as one of the country's most dangerous roads, with fatal and serious road accidents on the single carriageway between Perth and Inverness significantly higher than the national average.
Work on the new camera system saw columns, cameras and infra-red lighting masts erected on the single carriageway sections.
Earlier this year, figures suggested that the presence of the newly-installed cameras was already cutting drivers' speed - even though they had not been switched on.
Commenting on the pilot HGV project, Transport Minister Keith Brown said last week: "We want to see reliable and competitive journey times for all road users, including the freight haulage industry.
"Simply raising the speed limits for HGVs could have a detrimental effect, but the use of average speed cameras as part of the pilot helps support the wider changes we are making to promote an overall improvement in driving conditions.
''The 50mph HGV pilot will bring operational benefits and help reduce frustration on Scotland's longest road.''
Environmental group WWF Scotland has called for average speed camera schemes to be introduced on more of the country's roads and motorways "to help save lives and cut pollution''.
Climate and energy policy officer Gina Hanrahan said: "Alongside the clear safety benefits, enforcing speed limits on trunk roads using average speed cameras and other tools is an effective and cost effective way to reduce climate emissions as well as fuel costs for motorists.
"To reduce health-threatening levels of air pollution and meet our climate targets, the use of average speed cameras and other approaches to help reduce excessive speeds should be seriously considered on other major roads across Scotland.''
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.
Holyrood's Sport Committee has warned the Protection of Vulnerable Groups (PVG) system "may not be preventing unsuitable people from doing regulated work''.
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