One in nine (11%) vehicles on UK motorways drift out of their lanes, according to new research.
Analysis of more than 70 hours of footage found that the majority (53%) of incidents involved vehicles being driven in the middle lane.
Direct Line Car Insurance, which commissioned the study, warned that poor lane discipline could cause fatal crashes and lead to motorists being prosecuted for careless driving.
One of the biggest triggers was when cars were alongside lorries and overcompensated for the larger vehicle.
Drifting can cause a domino effect when vehicles are travelling in parallel across multiple lanes, meaning motorists in the outside lane are forced off the carriageway to avoid a collision.
Researchers analysed footage from the M40, M25, M4, M3 and M12 motorways.
A survey of 2,005 UK adults found that more than half (51%) had experienced another vehicle drifting into their lane on a motorway or dual carriageway in the past year.
The most common reason given for drivers who admitted to drifting was loss of concentration (48%), followed by lanes being too narrow (34%) and tiredness (29%).
Other causes included being distracted by passengers (15%), driving too close to the car in front (10%), changing music (7%) and programming a sat nav (6%).
Rob Miles, director of car insurance at Direct Line, said: “Failing to stay in your lane, even just for a split second, has the potential to cause a fatal accident when travelling at high speeds on a motorway.
“If drivers feel tired or are struggling to maintain their focus then they should find a safe place to pull over and take a break.”
He added that the research highlighted the benefits of features which assisted drivers to stay in their lane and warn them when they drifted.
“We would strongly recommend that those in the market for a new car consider a model with this technology,” he said.
“It could be the difference between having an accident or avoiding one.
“That said, we urge motorists to remain vigilant at all times and not to rely solely upon car technology to ensure their safety and that of other road users.”