Average speed cameras on the notorious A9 are not expected to become operational until the autumn and not the summer as originally planned due to technical problems.

The devices will also only be installed on single carriageway sections between Perth and Inverness.

Transport Minister Keith Brown had previously said that he hoped the first of the devices would become fully operational by the summer months when the road is at its busiest.

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However, chairman of the A9 Safety Group, Stewart Leggett, said: "We are moving on from the design phase to the introduction of the equipment itself. We expect it to be operational in October."

The new system was announced last year as an interim safety measure until the road is upgraded to a dual carriageway all the way to Inverness by 2025.

It originally said the system would operate on the 136 miles from north of Keir Roundabout at Dunblane to south of Raigmore Interchange in Inverness with most observers believing it would be on single and dual sections.

Transport Scotland has now made it clear that on the 113 miles between Perth and Inverness, there will be seven distinct average speed camera system zones, all of which will be on single carriageway sections.

There are about 80 miles of single carriageway on this stretch of the A9. The cameras are expected to be three to four-and-a-half miles apart.

Between Perth and Dunblane, which is all dual carriageway, there are expected to be 14 camera locations about the same distance apart.