Laws allowing lorry drivers to travel at 50mph on single carriageway sections of the A9 have been rubber-stamped by Scottish ministers.
The new speed limit will come into force at the same time as the average speed camera system on the route becomes operational, October 28.
It is hoped that the pilot, which was approved by the Scottish Parliament earlier this year, will help improve safety on the route between Perth and Inverness by reducing the frustration felt by drivers who find themselves stuck behind and HGV.
Transport Minister Keith Brown said: “This pilot is part of a package of measures that is being taken forward to improve the operational performance of the A9 and to enhance safety.
“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.”
Richard Burnett, chief executive of the Road Haulage Association, added: “Many A9 incidents, together with the resultant delays, are caused by no more than sheer motorist frustration when getting stuck behind a slow moving heavy goods vehicle.
“It makes sense that a 10mph reduction in the speed differential between cars and HGVs will mean a corresponding reduction in frustration and accidents.”