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?

Highway hypnosis, also known as white line fever, Road Hypnosis is an altered mental state in which a person can drive a car, truck, or other automobile great distances, responding to external events in the expected, safe, and correct manner with no recollection of having consciously done so. In this state, the driver’s conscious mind is apparently fully focused elsewhere, while seemingly still processing the information needed to drive safely. Highway hypnosis is a manifestation of the common process of automaticity.

The concept was first described in a 1921 article that mentioned the phenomenon of “road hypnotism”: driving in a trance-like state while gazing at a fixed point. A 1929 study, Sleeping with the Eyes Open by Walter Miles, also dealt with the subject, suggesting that it was possible for motorists to fall asleep with their eyes open and continuing to steer. The idea that the unaccountable automobile accidents could be explained by this phenomenon became popular in the 1950s. The term “highway hypnosis” was coined by G. W. Williams in 1963. Building on the theories of Ernest Hilgard (1986, 1992) that hypnosis is an altered state of awareness, some theorists hold that the consciousness can develop hypnotic dissociation. In the example of highway hypnosis, one stream of consciousness is driving the car while the other is dealing with other matters. Partial or complete amnesia related to the time spent driving under highway hypnosis can develop for the driver involved.

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.