Plans to reduce traffic congestion by forcing lone drivers to use slow lanes on Scotland's busiest motorway could cause more jams, a motoring group has warned.

Under proposals given the green light by the Scottish Executive, a section of the A8 to the north east of Glasgow will be upgraded to a three-lane motorway by 2010.

The executive said that it was considering new methods of ensuring that drivers carrying passengers were given "fast-track" access to this new section of the M8 motorway.

Drivers without passengers would be filtered into specific lanes before they join the motorway, where they would face extra traffic lights as other vehicles are given priority.

I really don't see how you could sort people out before you get to the road without causing artificial congestion Neil Greig AA

AA Scotland's head of motoring policy, Neil Greig, said giving priority to higher occupancy vehicles could work.

However, he suggested the executive's proposal "still appears sketchy, and seems to be a very complicated way of going about it".

He said: "High occupancy vehicle lanes have worked in America on long city-to-city routes, and if implemented properly they could offer the incentive to car clubs which they don't really have at the moment.

"But the concern is that it seems to be more about sorting the traffic into different lanes before it gets onto the motorway.

"I really don't see how you could sort people out before you get to the road without causing artificial congestion."

Detailed consideration

The upgrade of the A8 is a 10km section between Baillieston on the outskirts of Glasgow and Newhouse in North Lanarkshire.

It was among a number of road and rail schemes given the green light under a £450m funding package announced by Transport Minister Iain Gray on Wednesday.

The lane diversion proposals are also being considered for a new section of motorway between Stepps and Haggs, where the A80 will be upgraded to link the two existing sections of the M80.

A Scottish Executive spokeswoman said: "These proposals are being looked at as part of the corridor studies in an effort to help manage traffic on busy roads, and more detailed consideration is still required."