A senior psychologist at the Health and Safety Executive said that Larry Harrison, the driver of the Great Western express who jumped a red light, may have been suffering from the kind of "gaps or lapses" which can last between five and 15 seconds.
In written evidence to the inquiry, Dr Deborah Lucas said that people can appear to be attentive with their eyes open and with "no loss of posture", but with much lower alertness. Mr Harrison may also have been suffering from "post- lunch dip", Dr Lucas told the hearing into the disaster, in which seven people died and 150 were injured.
The absence of an automatic warning system (AWS) on the express, which had been switched off because it had developed faults, prevented the driver from noticing his failure to respond. Mr Harrison, whose Paddington-bound service smashed into a freight train coming in the opposite direction, passed through two double yellow and a single yellow cautionary light before he braked too late at a red signal.
While there may have been a range of contributory factors, there was no single reason why Mr Harrison did not respond to the signals, the inquiry was told. The AWS sounds a bell when a train is approaching a green light, but a klaxon when there are warning lights ahead. Dr Lucas said that micro- sleeps were more likely where tasks were prolonged - half an hour or more - which were familiar to the person concerned or "monotonous".
Nevertheless, Mr Harrison's journey that day was not routine and may have been more "challenging" because there were additional tasks to be undertaken due to the faulty AWS. Commenting on an arrangement promoted by the train drivers' union Aslef, Dr Lucas said that having a second person in the cab when safety devices are unavailable, would not necessarily improve "levels of human reliability". It was possible that "social interaction" would limit the beneficial impact of a second person.
Training employees for working without AWS would not normally solve the problem, since drivers would revert unconsciously to thinking that the system was in operation. Introducing speed restrictions under such circumstances would probably reduce risks, but might also increase "boredom levels".
Professor John Groeger, of Surrey University, told the hearing that any experienced train driver would have "considerable difficulty" in operating for an extended period without the safety system.Reuse content