Rail safety: more flaws revealed

Railtrack bungled the installation of the UK’s new rail safety system, so that it now encourages train drivers to accelerate towards the buffers at terminus stations, The Engineer can reveal.

The new Train Protection and Warning System (TPWS), designed to apply the brakes automatically if the train is travelling too fast, was calibrated incorrectly at the approach to a number of stations including Waterloo main line.

The system was set to stop trains travelling at more than 6.5mph, which forced drivers to bring the train to a virtual halt before reaching the platform. The result was that after passing over the speed loops, drivers would regularly have to accelerate towards the buffers, a manoeuvre that increases the risk of a crash and is strictly forbidden.

The speed loops – which were fitted by Jarvis, AMEC, Amey, First Engineering and Carrillion – were never tested to operate at speeds of below 10mph, according to Douglas Steptoe, a systems engineer at French engineering company Thales, which supplied the TPWS equipment. ‘The loops were fitted outside their area [of operation], by setting them at 6.5mph. They were never tested below 10mph because the system wasn’t intended for that,’ he said.

Before TPWS drivers arriving at stations disengaged the engine from the wheels and coasted the train into the platform, braking as the buffers got closer.

The problem of brake triggering arose as TPWS was being installed across the UK network a year ago. South West Trains’ drivers reported having to accelerate towards the buffers at Wallersash junction, Mitcheldever, Portsmouth Harbour, Southampton, Fareham and Waterloo. The train operator’s head of drivers confirmed that Waterloo has been particularly problematic, as drivers must accelerate to climb a slope before reaching the buffers.

Since then Network Rail, which took over from Railtrack, has been modifying the triggers, known as ‘overspeed loops’, to 10mph. Trials were conducted at Charing Cross last summer, and Network Rail claims all stations with rectangular loops have been upgraded.

But the new 10mph limit has not solved the problem on slam-door trains, of which South West Trains has 145, as their speedometers are so unreliable that drivers have difficulty knowing the difference between 5mph and 10mph, said a spokeswoman. ‘This occurs on old rolling stock because they have non-calibrated speedometers.’

The speed loops encourage impatient passengers to jump from trains as they move at 5mph towards the buffers, increasing drivers’ safety concerns.

But the safety system cannot be removed to aid the drivers as the Health and Safety Commission recently ruled that all mark-one trains must be fitted with TPWS, in response to the train operating companies’ resistance to reinforcing the structure of the vehicles as a safety measure against collisions.

Thales engineers suggested a new speed limit of 15mph, but Network Rail rejected this as a review carried out by the firm found a significantly higher risk of passenger injury if trains hit buffers at 15mph.

TPWS will be the UK’s rail safety system for the next 10-15 years, until the more advanced European Rail Traffic Management System (ERTMS) is installed.

How TPWS works

The 1999 Railway Safety Regulation requires TPWS to be fitted to all train lines by 1 January 2004.

The technology combines a train stop system with a speed trap, which can be set up to 350m away from the signal. It requires no action from the driver, but forces any train travelling at 75mph to brake at 350m from a red signal.

TPWS has both onboard and track-based equipment. The track-based system consists of loops, or rectangular-shaped cables that sit between the rails and carry a circuit that is detected by the train equipment if a signal is red. These come in two forms: overspeed loops, which sit at the signal, and trigger loops, installed 350m back from it. The trackside equipment links the loops to a computer network for monitoring the rail system.

The train-borne device is based on an antenna, attached to a bogie, for detecting the loops, and a control system linked to the train’s control panel. If TPWS is triggered the train brakes are applied for 60 seconds to bring it to a stop, and the driver cannot accelerate for 60 seconds once he has pushed an acknowledgement button.

A more advanced version, TPWS Plus, includes extra speed traps up to 1.5km away from signals for a train travelling at 125mph. A Network Rail spokesman said the system has not yet been installed, and scope for its usage on high-speed lines is still being defined.

TPWS-E, a still more advanced system compatible with ERTMS, is being developed. This uses trackside transponders linked to train and track control, and speed traps.