At around 03:30 hrs on Sunday 16 May 2021, a road-rail vehicle ran away while being on-tracked at a road-rail access point near Belle Isle Junction in north London. The RRV ran downhill for approximately 600 metres before coming to a stop in a tunnel. Although no one was injured, the operator jumped from the road-rail vehicle before it entered the tunnel.
The road-rail vehicle ran away because it entered service with ineffective rail-wheel brakes and staff working with it were unable to stop the runaway. The brakes were ineffective because a valve in the braking system had been left open following maintenance. 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.
RAIB has made two recommendations. One is addressed to the company which designed and fitted the direct rail wheel braking system, to revise its process for risk assessment, and the second to the owner of the machine, to review its strategy for confirming the ongoing integrity of the direct rail wheel brake system.
Additionally, two learning points have been identified. These reinforce the importance of organisations which design and implement changes to on-track plant sourcing the original design information to inform their decisions, and of those supplying and operating road-rail vehicles ensuring that suitable facilities are available for in-service testing.