A £250,000 system is due to be installed this summer on the A82 and A85 between Tyndrum and Lix Toll, near Killin.

News of Scotland’s fourth such scheme comes months after The Scotsman revealed transport secretary Michael Matheson was “actively looking” for more sites for such cameras.

They measure a vehicle’s speed over a set distance, with the latest cameras to be positioned along a 16-mile stretch of the two trunk roads, which are in the Stirling council area.

A82 Road from Tyndrum towards Crianlarich

Mr Matheson said the move was justified because two people were killed, 21 seriously injured and 12 slightly hurt over that section from 2014-16 – the most recently assessed period.

James Whiteside, 59, and Jacqueline Hennessey, 54, died when their motorbike collided with a car on the A85 just east of Crianlarich in 2015.

The incident was among 21 crashes over the three-year period.

The incidents have come despite mobile speed camera vans patrolling the route, where up to one in three drivers are known to speed.

Speeding and casualties have been significantly cut on Scotland’s average speed camera systems since the first was established on the A77 in Ayrshire in 2005.

The A9 between Dunblane and Inverness followed in 2014, with the A90 between Dundee and Stonehaven being added two years ago.

Mr Matheson said: “We already know from our experience with average speed cameras successfully deployed elsewhere that they encourage improved levels of driver behaviour, with a 60 per cent reduction in the number of killed or seriously injured casualties on similar rural single carriageways.

“This investment will deliver a range of benefits for road users.

“This includes reducing road casualties, improving journey time reliability and reducing the frequency of incidents and disruptive closures.”

The IAM RoadSmart motoring group said average speed cameras would bring benefits but were not a panacea.

Neil Greig, its Scotland-based policy director, said: “There is no doubt they will deliver fewer serious casualties and a calmer atmosphere on these key economic routes to the Highlands.

“They won’t totally eliminate junction crashes, fatigue-related crashes or the general human errors drivers make below the speed limit.”

Mr Greig said the 50mph lorry limit should also be extended from the A9 to all Scottish single carriageways, like in England. Transport Scotland said it was awaiting evaluation of the increase from 40mph south of the Border.

Four people were killed on Scotland’s roads between Friday and Saturday. A car driver collided with a pick-up in Ellon, a couple were hit by a car in Glenrothes and a 75-year-old woman was struck by a quad bike in Glasgow.

New average speed cameras to track motorists on key route to Highlands