Sarawut Songsivilai, the department's director-general, said 30% of car accidents on highways are caused by motorists driving too slowly in the far-right lane, which has been designated for fast-moving vehicles.
That made it the No.2 cause of accidents, following cars veering off roads which account for 45% of accidents.
“If a motorist in an outer lane is driving slowly the driver behind will try to pass on the inside lane where his view of traffic in front will be obscured, which often leads to cars colliding,” he said.
“Proposed new speed limits for outer lanes will be clearly marked and are designed to lower the chances of sideswiping or rear-ending,” he added.
Mr Sarawut said this is in line with the Transport Ministry's plan to cut car accidents.
The ministry is reportedly looking at raising the speed limit for the outer lane on major roads and highways to at least 90kph. The new speed limit reportedly will be introduced on roads with four lanes or more.
Currently, the speed limit on such roads, mostly in cities, is 80kph. Once new limits are in place, slow drivers will face legal penalties on par with speeding offenders.