Severn Tunnel rail accident

The Severn Tunnel rail accident occurred in the tunnel on 7 December 1991.[1]

The 08:30 London Paddington to Cardiff Central operated by an InterCity 125 was stopped at a signal guarding the entrance to the Severn Tunnel. On telephoning the signalman according to Rule 55, the driver was advised of a signal failure and given permission to proceed slowly at caution. Three miles into the tunnel, the train was struck from behind by a Class 155 Sprinter travelling from Portsmouth to Cardiff. 185 passengers were injured, including five seriously, but none fatally.[1]

Because track circuits were unreliable in the unusually wet tunnel environment (10 to 20 million gallons of water are pumped out per day),[2] axle counters were used instead. The official report into the accident[2] could not reach a firm conclusion, but speculated that the cause was either:

• an unaccountable error on the part of the Sprinter driver, or:
• technicians in the relay room at Severn Tunnel Junction had reset the axle counter while investigating the earlier signal failure fault, thus clearing the signal for the Sprinter.[1]