Commuters on Britain's rush-hour roads and railways suffer greater anxiety than fighter pilots or riot police facing angry mobs of protesters, according to research published today which suggests that many travellers retreat into a "light hypnotic trance" as a defence mechanism.

Psychologists found that travellers tackling peak-hour congestion experienced heart rates as high as 145 beats per minute, compared to an "at rest" rate of 65 for a healthy young adult.

Volunteers in the study agreed to wear caps with electrodes attached to their heads on their daily journey to work, usually concealed under a baseball cap to avoid curious looks from fellow travellers.

Researchers discovered a surge in cortisol, a hormone secreted when the body is under pressure. They also detected signs that commuters' brains briefly turned inwards and shut down to the outside world - a defence process dubbed "commuter amnesia".

Dr David Lewis, who carried out the research for the technology firm Hewlett Packard, said: "Many commuters go into a sort of inner world when they're travelling and don't really notice what's happening around them. They shut everything out to take themselves away from a world they find aversive."

He said the symptoms of stress were equivalent to those measured in his past studies using combat pilots and police officers. But for commuters, the experience is worse because of a sense of "impotence".

"Stress is worst when we want to achieve something but we're being stopped from doing so," said Dr Lewis. "The maximum stress would be for somebody on their way to an important meeting when a train just stops in a tunnel, or the traffic stacks up on the motorway."

One in five of Britain's trains typically runs late. According to the National Audit Office, 13% of trunk roads are congested on at least half of the days of the year.

MPs on the transport select committee suggested last year that congestion had become so bad that many commuters faced a "daily trauma" in getting to work.

However, experts expressed caution about today's findings. Edmund King, executive director of the RAC Foundation, said the popular take-up of mobile phones had eased pressure for travellers who were at least able to warn colleagues if they were running late.

While he agreed that delays caused great anxiety, he suggested that they were so regular that they had lost some of their impact: "Congestion is such an everyday occurence that I think a fighter pilot has got to be suffering more stress than a normal M6 commuter."