On this day in 1991, two passenger trains collided inside the Severn Tunnel, leading to one of the most notable rail accidents in the tunnel’s history. The crash occurred on 7 December when a Regional Railways Sprinter ran into the back of an InterCity 125 service already travelling through the tunnel. Although injuries were widespread — a total of 185 people hurt, including five seriously — all passengers and crew survived.

The Severn Tunnel, which forms a key link beneath the River Severn on the South Wales Main Line, is over four miles long and is constantly affected by water ingress. To keep it operational, powerful pumps remove millions of gallons of water every day. Track circuits inside the tunnel had previously experienced issues in damp conditions, leading to the introduction of axle counters in 1987 to monitor train movements more reliably.

A signalling fault was first reported during the afternoon of 6 December, and with the issue still present the next morning, trains entering the tunnel were required to receive verbal authorisation to pass a signal at danger. At approximately 10:20 am on 7 December, the InterCity 125 — operating from London Paddington to Cardiff — halted at the tunnel entrance signal and, after speaking to the signaller, was granted permission to proceed into the tunnel.

Around three miles inside, the Sprinter service from Portsmouth Harbour to Cardiff struck the rear of the InterCity train. The collision caused the InterCity’s automatic brakes to apply and bring the train to a stand. The driver broke the emergency tell-tale wire fixed along the tunnel wall to send an alarm signal and then used a tunnel telephone to report the collision. The rear power car of the high-speed train became detached, but neither train derailed and the rolling stock remained upright within the tunnel.

Emergency trains were dispatched from both ends of the tunnel, though access to the scene took at least two hours. The most seriously injured passengers were evacuated first. Around three hours after the impact, those on the Sprinter were moved into the InterCity 125, which was then carefully driven out of the tunnel at approximately 5 mph. The full evacuation of uninjured passengers took around six hours, and rail services resumed through the tunnel in under 48 hours.

The official investigation, carried out by the HM Railway Inspectorate and released in 1994, could not reach a firm single conclusion. It determined that the circumstances most likely involved either an unexplained error by the Sprinter driver or accidental resetting of the axle counter equipment by technicians investigating the earlier signal fault, which may have cleared the section incorrectly. More than thirty years later, the Severn Tunnel collision is still referenced as an event that highlighted the challenges of signalling reliability in demanding environments and the importance of robust safety procedures.