US & Canada

'Positive Train Control' could have prevented US derailment

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Media captionA 45-second look at how Positive Train Control works

The investigation into the cause of a fatal train derailment in the US city of Philadelphia this week has already yielded its first conclusion: it could have been prevented with technology.

"Positive Train Control" is a digital system that allows trains to communicate with each other and can automatically stop or slow the train if danger is detected.

"We feel that had such a system been installed on this section of track, this accident would not have occurred," said accident investigator Robert Sumwalt of the National Transportation Safety Board.

The system monitors regional speed limits, works zones and other operational data using Wifi, GPS, and radio transmissions according to the Association of American Railroads.

A human engineer remains in control of the train but can be overridden by Positive Train Control (PTC) if sensors on the train and along the track notice that the train is moving too fast or heading into a danger zone.

Investigators in Philadelphia report that the derailed train, which killed at least eight people, was travelling at more than 100 mph (160 km/h) when it entered a curve - over twice the speed limit for that stretch of rail.

Congress mandated in 2008 that railways be equipped with PTC after a head-on collision between two trains in California that investigators determined was caused by the engineer running past a stop signal while texting on his mobile phone.

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Image caption The recent crash near Philadelphia killed seven and injured over 200

December 2015 is the deadline to outfit more than 600,000 miles of US railways with PTC, but experts say that it is unlikely that the deadline will be met for one reason - a steep price tag - about $10bn (£6.35bn).

The Philadelphia railway, as well as those that carry passengers or hazardous materials, are required by Congress to equip the technology.

Amtrak, which operates the Philadelphia commuter railway, has so far equipped about 400 miles of track with PTC sensors.

Completing PTC installation would require training for 180,000 employees, new equipment added to 22,500 locomotive, and 30,000 new wireless antennae, according to the Association of American Railroads.

"A national-wide PTC system built, installed, tested, and approved on this scale simply cannot happen by the 2015 deadline," they claim.

A Spanish train derailment in 2013, which occurred while the engineer was in control of the steering, prompted authorities to install automatic braking at the curved section of the track where the crash occurred.

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