Shortly before 07:00 hrs on Friday 13th August 2010, an engineering train ran away along part of the Northern Line of London Underground.
The train consisted of a self-propelled diesel-powered unit designed for re-profiling worn rails. It had been working between Highgate and Archway stations on the southbound line during the night of 12/13 August. At the end of grinding operations that night, the crew of the unit found that they were unable to restart its engine to travel away from the site of work.
An assisting train, consisting of a six-car train of the 1995 stock used for passenger services on the Northern line, was sent to the rescue of the grinding unit. The assisting train was coupled to the grinding unit by means of an emergency coupling device, and the braking system of the grinding unit was de-activated to allow it to be towed. The combined trains then set out to run to East Finchley station. At about 06:42 hrs, after passing through Highgate station, the coupling device fractured and the grinding unit began to run back down the gradient towards central London. The crew of the grinding unit, who had no means of re-applying the brake, jumped off the unit as it passed through Highgate station. It then ran unattended for about four miles, passing through a further six stations, and came to rest near Warren Street station about sixteen minutes later. LUL control room staff took action to clear trains away from the path of the runaway unit.
No-one was hurt. There was some damage to the grinding unit, and points at Mornington Crescent station were damaged when the unit ran through them.
The emergency coupling broke because it was not strong enough for the duties it was intended to perform, and had been inadequately designed and procured. RAIB has made seven recommendations to London Underground Ltd, covering the processes for introducing new engineering equipment, review of existing equipment, investigation of incidents, training of staff, the operation of unbraked vehicles, and the quality assurance processes used by LUL and its associated companies.
Response to recommendations:
- RAIB will periodically update the status of recommendations as reported to us by the relevant safety authority or public body
- RAIB may add comment, particularly if we have concerns regarding these responses.