The incident has prompted a warning to machine owners to check their brakes properly.
The investigation began after the runaway of a road-rail vehicle (RRV) at around 03:30 hrs on Sunday 16th May 2021, while being on-tracked at a road-rail access point near Belle Isle Junction in north London. The RRV ran downhill for 600 metres before coming to a stop in a tunnel. The operator jumped off before it entered the tunnel and no one was injured.
Investigators found that the vehicle ran away because it was put into service with ineffective rail-wheel brakes; staff working with it were helpless to stop the runaway.
The RRV was a ProMax mobile elevating work platform (MEWP) modified in 2014 by Allan J Hargreaves (AJH) Plant Engineers with its own design of direct rail wheel braking system (DRWB).
Pod-Trak owned, maintained and supplied the vehicle. It also employed the machine operator, the plant operations scheme representative and the maintenance fitter.
Morgan Sindall Infrastructure was a principal contractor to Network Rail for the King’s Cross remodelling project, on which the vehicle was being used.
The brakes were ineffective because a valve in the braking system had been left open after maintenance work. The possibility of this had not been recognised during the design or risk assessment of the brake system, and the situation had not been identified during operation or regular in- service testing.
Two underlying factors were identified. These were that the risk assessment undertaken in support of a modification to the machine to fit a direct rail wheel braking system was incomplete, and that the company responsible possibly did not have a thorough understanding of the unmodified machine or its original conversion for rail use.
The Rail Accident Investigation Branch (RAIB) has made two recommendations. Hargreaves was advised to revise its process for risk assessment; Pod-Trak, as owner of the machine, was advised to develop systems that prevented machines being sent out with faulty brakes.