According to the AA, if other drivers were more aware of the speed limit for lorries on single carriageway roads it would lower the risk of road rage and accidents.
Launching a survey to mark last month's 80th anniversary of the introduction of driving licences for lorry drivers, however, it found that 81% of drivers did not know that the limit for lorries on such roads is 40mph.
Scottish drivers (40%) showed the highest level of knowledge while only 14% of those questioned in Northern Ireland were able to come up with the right answer.
Drivers in managerial or professional roles were the least (16%) able to identify 40mph while even the group which did best, skilled manual and service workers, could only muster 26% who knew the correct speed limit.
Jim Kirkwood, AA DriveTech managing director, said: “Many drivers say they feel intimidated by lorries. But this research highlights how a lack of understanding of the laws surrounding lorries, and how best to drive around them, could be contributing to this."
Lack of knowledge of speed limits for other vehicles can cause problems and frustrations on the road, he stressed.
Proposals to raise the speed limit for lorries on single carriageway roads to 50mph have been consulted on by the Government, but no decision has been announced. Part of the reason for investigating a possible change was to reduce the build-up of traffic travelling behind lorries on single carriageway roads.