An improved ultrasonic testing regime has been introduced on the London Underground following the Hammersmith derailment a year ago. 

The investigation report confirmed that the cause of the derailment was a broken rail, but concluded that visual inspection and ultrasonic testing practices (preceding the incident) would not have picked up the defect prior to the rail breaking. 

Now Metronet Rail and Tube Lines have introduced a road-rail vehicle to undertake ultrasonic inspections as an interim measure to improve the frequency and quality of track inspections while the two companies develop a fully automated train equipped with ultrasonic and track recording equipment which can run during the passenger service.

The road-rail vehicle, a modified Land Rover developed by Sperry Rail, tows a trolley fitted with ultrasonic detection equipment to identify track irregularities at an early stage.

At present, rail flaw detection on the Underground is carried out manually using hand-held ultrasonic detection devices. A team of three or four workers can inspect over three miles of rail in a four-hour night shift. 

The new ultrasonic Land Rover travels at up to 10mph and can cover 12.5 miles during an "engineering hours" shift, quadrupling the distance tested manually.

The vehicle ultrasonically inspects, creates, displays and stores data from both rails simultaneously and can detect the full suite of rail defects during one inspection. In addition, rail depth can be measured every 5mm along the track, identifying rail wear and corrosion. 

"This is an important step forward in achieving our long term goal of zero broken rails," said Metronet Rail's director of safety and assurance Ian Prosser.

Stephen Peat, Tube Lines director of operations said: "This development will really help us modernise the way the Tube is maintained."

Types of defects identified with the new vehicle include:  Defects in the rail web, including bolted joint, insulated rail joints,  switches and crossings and defects that originate from the rail foot once it extends into the area under the web - as was the case with Hammersmith derailment in October 2003.

Ultrasound or high frequency sound waves, above the frequency of human audibility, is emitted by an ultrasonic transducer, passed through the rail at a calculated distance and an echo of that sound is expected back. 

Defects are identified when the ultrasonic beam is interrupted on its way through the rail and returned sooner than calculated.  By accurately plotting the amplitude and range of the signal the size of the defect can be estimated.

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The day after this announcement, Tube Lines said it had made profits of £100,000 a day.

The figures immediately prompted renewed criticism of the Government's controversial public-private partnership on the Tube which was opposed by mayor Ken Livingstone.

Tube Lines - which received £360million of public money during the year - made an annual profit of £41million up to March 2004.

Tube Lines chief executive Terry Morgan received a pay package of £552,00, including a performance bonus of £100,000.

RMT general secretary Bob Crow said PPP is expensive for taxpayers yet produces risk-free profits for the companies involved.

London Underground has accused both Tube Lines and Metronet of producing "non existent, incompetenet and inconsistent" work plans and of often failing to finish engineering work on time.

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