Rail freight

28.02.18

Uneven load and track twist led to Lewisham freight train derailment

A freight train derailment in south London occurred when an unevenly loaded wagon encountered a “significant track twist”, the Rail Accident Investigation Branch’s (RAIB) investigation has found.

Two wagons within an aggregate train derailed on newly-laid track at Courthill Loop South Junction in Lewisham last January.

The first wagon derailed, damaging the track, and then overturned, spilling its payload of sand.

Major disruption was caused on some of the busiest commuter routes in the country, although no one was injured.

The new track, which was made up of separate panels of switch and crossing track, had been installed 10 days earlier.

Most of the track panels were preassembled prior to arrival at the site, and a mechanical connector called a bearer tie was used to join the concrete bearers, designed to support rails on more than one panel - a concept referred to as ‘modular S&C’, originally developed by Network Rail.

The following weekend planned follow-up engineering work was carried out and the derailment occurred the day after the hand-back checks had confirmed that the track geometry was suitable for the passage of trains.

Investigators found that the first of the two derailed wagons, which was probably carrying an uneven payload, encountered a significant track twist, which resulted in insufficient wheel load at the leading left-hand wheel to prevent its flange climbing over the rail head.

The track twist had developed quickly following the hand-back because the support offered by the track bed to the concrete bearers was poor and the inherent flexibility of the bearer ties between the two running rails made one side more susceptible to the poor track bed than the other.

RAIB found that Network Rail’s engineering processes for specifying and developing modular S&C layouts were an underlying factor as they were inadequate for controlling the risks associated with flange climb derailment.

Following its investigation RAIB made recommendations to Network Rail, raising concern with its processes to identify and mange risks associated with vertical track geometry features following track renewal and heavy maintenance, and the design and validation of its modular S&C layouts.

Its recommendation to RSSB is concerned with understanding and managing the derailment risks associated with uneven loading.

Simon French, chief inspector of rail accidents, called the incident “particularly disappointing” given the recent track renewal, adding that the designers of the new layout had not fully understood how the assembly could behave if the track bearers were not fully suspended.

“The track was poorly supported when it was handed back for traffic on the day before the derailment, because there had not been time for the machines to finish tamping the ballast, and manual consolidation work was ineffective,” he said.

He concluded: “It is of concern to me that, although the railway industry has established a working group to examine these issues, it remains unclear how its findings will be translated into actions to mitigate the risk of freight train derailment.”

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Comments

R Nosgrove   01/03/2018 at 08:27

Summary and link to the RAIB report here: https://www.gov.uk/government/news/report-042018-freight-train-derailment-at-lewisham

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