Disaster could have been avoided

As Railtrack reels from the Potters Bar rail tragedy we reveal that a preventive technology is already working in the UK.

A new high-performance points system that would have prevented the accident at Potters Bar is already being installed in areas of the UK’s rail network, The Engineer can reveal.

The points at Potters Bar were to be replaced by the new safer system, but only after they had served their 20-year life span. By the time of last week’s crash that killed seven people, they were just eight years old. A spokesman for Railtrack said while new technology was useful, costs might be prohibitive to its timely installation.

‘Technology is changing all the time, and as technology improves we install it. But there are obviously costs involved, and we are always looking to the government for more money.’

Continuous monitoring

The technology, developed by IAD Rail Systems, continuously monitors the position of rails within the points to alert staff if they move out of position, and is capable of detecting loose stretcher bars.

The West Anglia Great Northern train travelling from King’s Cross to King’s Lynn was derailed when a set of nuts attached to two stretcher bars became loose, allowing the locking stretcher bar to buckle when the train passed through the points.

But IAD director Mick Ledger said there was a ‘good chance’ that the movement of the stretcher bar would have shown up had the area been fitted with the new switch system.

‘Anything outside the window (the system’s safety parameters) would have been flagged up by a loss of detection,’ he said.

All points systems are locked when a switch rail is moved across to meet the main rail and secured by pins. IAD’s system includes detectors on the main rail, which give continuous measurements of where the switch rail is in relation to it.

If there is an obstruction or gap of more than 3.5mm between the two, which could cause a train to derail, detection is lost and signal staff are alerted.

The system has already detected a loose stretcher bar on a set of points near Tamworth in Staffordshire, said Ledger. ‘If you were continuously monitoring the system, you would definitely see the stretcher bar was moving more than was normal.’

Around 40 of the new systems have been installed across the UK rail network, including some on Virgin Cross Country routes.

‘Railtrack has been putting them in wherever there is a [points] renewal, on either a high speed line or an area of high traffic volume,’ said Ledger.

Less prone to failure

IAD’s system is designed for a 25-year life, with no scheduled maintenance required, although annual checks are still needed to check for broken parts.

While more expensive than existing points systems, it is less prone to failure, and this higher reliability means Railtrack is planning to change 15-20 per cent of points on the network over to the new system as they reach the end of their life or need upgrading, such as those on the planned West Coast Main line modernisation.

Many existing points are based on hydraulics, which can be prone to failures or leaks, but the new system uses electro-mechanical technology. The system has also been designed to withstand flooding, while the amount of power that drives its motor is controlled to prevent overheating.

Sidebar: How did the nuts come loose

The investigation into the rail accident at Potters Bar was this week focusing on a set of loose nuts at the points, causing the train to be derailed.

The interim HSE report into the accident, published this week, found the nuts on two stretcher bars were detached, putting the locking bar connecting the tips of the points under a level of pressure normally shared by the stretchers. The bar buckled under this extra strain, causing the points to move as the rear of the four-car West Anglia Great Northern train’s third carriage passed over them. The rear carriage then derailed, skidding left, and ended up on its side wedged under the station canopy.

The HSE investigation team will now continue with its examination of the set of points, and plans to review maintenance schedules and records relating to the equipment.This investigation is likely to focus on two of the four detached nuts, which rail maintenance contractor Jarvis admitted this week were found to be loose nine days before the accident.

The nuts were discovered to have come loose during a routine maintenance checkon 1 May, and were replaced.

British Transport Police will examine the nuts, to look into the possibility that their threads could have been worn, causing them to come loose again with the vibrations of trains travelling over the points.

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