TRAINS will run with a shorter safety gap to the one behind under a new control system that squeezes more capacity from tracks.

Network Rail is planning to test the system in North Wales before installing it on high-speed lines.

All trackside railway signals will be removed and replaced by a digital radio link and sensors between the rails which tell each train exactly how far ahead the next train is. If a driver makes an emergency stop the change of speed will be communicated instantly to the train behind and the brakes will automatically engage.

The system, known as the European Rail Traffic Management System (ERTMS), also calculates the highest speed at which a train can safely travel without catching up with the train in front.

On some sections of line the distance between trains will be halved, but a minimum safety gap will be retained to allow for differences in the braking capacity of trains and tracks made slippery by ice or leaves.

The system will also remove the small remaining risk of drivers running past red lights and hitting another train, the cause of seven deaths at Southall, Middlesex, in 1997 and 31 at Ladbroke Grove, West London, in 1999. An automatic braking system has been installed on most of the network but is fully effective only at speeds below 75mph (120kmph).

The system could allow high-speed trains to operate without drivers, but the industry believes that it will be many years before this becomes publicly acceptable.

At present, lines are divided into “blocks”, entry to which is controlled by signals. A train has to wait for the service in front to leave a block before receiving a green light to enter it.

On the East Coast Main Line, where a shortage of capacity means hundreds of passengers have to stand at peak times, the block system means that the minimum gap between 125mph trains is three minutes.

The time between trains will be cut to 2½ minutes, and could be further reduced when later versions of ERTMS are installed. The system will allow the East Coast Main Line to accommodate an extra four trains an hour at first and eventually an extra ten trains. It has already been introduced on the high-speed line between Rome and Naples, where trains run at 186mph without any signals to separate them.

Alstom, the company that installed the system, said that the extra cost was justified not only by improvements in capacity and safety but by also removing the need for maintenance of signalling equipment.

Network Rail will sign a £59 million contract next month to equip the Cambrian line, from Shrewsbury to Aberystwyth and Pwllheli. The line was chosen because it is a self-contained part of the network used by only a small of number of trains. The 12 trackside signals will be removed and the system will control the trains from December 2008.

Simon Kirby, Network Rail’s director of major projects, said a review of ERTMS in December would decide how to introduce it elsewhere. “Clearly we will go for a more complex line (than Cambrian) where there is more need to improve capacity for freight and passengers.”

Network Rail plans to announce options for equipping more lines in January. Colin Foxall, the chairman of the watchdog Passenger Focus, said: “We urgently need more capacity and this system is an alternative to building new lines, which are very expensive and often impractical.”

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