A train driver says he was experiencing “highway hypnosis” just prior to the derailment in which four people were killed last week in New York. So what is it?

This is what you sometimes experience as a driver when you can’t recall the previous few seconds of your journey, says Paul Watters of the Automobile Association in the UK. It’s more likely on mundane or familiar trips when you don’t need to take in the road signs.

“It’s a strange feeling. You’re not necessarily inattentive but you’re in a slightly different state. I don’t think it means you’re going to have an accident but it means you’re not completely engaged in the task of driving, so we would advise members not to get distracted like this.”

It does not mean you’re falling asleep, says Jim Horne of the Sleep Research Centre in Loughborough University, who adds that it’s like reading a newspaper at breakfast but you’re not taking in the words because you’re listening to what’s going on in the kitchen.

Driving long distances can cause the brain to behave in the same way as it does under meditation, says Stuart Robertson, a hypnotherapist in Edinburgh who specialises in treating drivers. In his view, it’s a relaxed state but if a dog was to run into the road, the driver could react as quickly as normal – or quicker, he believes – because the sub-conscious is still highly engaged with the environment.

But others do believe highway hypnosis causes accidents. Drivers who “zone out” have slower reaction times, according to Joshua Maxwell, an ergonomics engineer at the Hyundai-Kia Technical Center in Michigan, which has just begun a study measuring brainwave activity and creating some kind of warning system.

It could explain why at some accidents there are no skid marks before a car went into the back of a lorry on the hard shoulder, says Peter Rogers, chief examiner at the Institute of Advanced Motorists. Technological advances like cruise control are part of the problem, he says.

“If you’re in Leeds and set off to go to Carlisle, you have a long journey without much driving input required for a lot of the time.”