The European Train Control System (ECTS) Automatic Train Protection (ATP) technology is designed to override a train's controls and apply the brakes when it is about to pass a danger point or exceed the speed limit.

A spokesperson for RailCorp said one aspect of the trial is to establish how to deal with a failed signal, the cause of the 1999 Glenbrook accident that killed seven people.

She said that under the current trial set-up a train passing through a failed signal would enter a "staff responsible" mode under which it would be limited to 25km/h.

"In the Glenbrook case, the maximum speed of both trains would have been limited . . . so the driver of the second train would have a greater chance of pulling the train up in time," she said.

Group General Manager Asset Management for RailCorp, Gary Seabury, said the section of track between Penrith and Mt Victoria was ideal for the testing process.

"We chose this section . . . on the Blue Mountains line for its ability to test a diverse range of operating conditions found on the network without interfering with regular passenger services," he said.

"The test trains will operate between timetabled services and will not carry CityRail passengers."

"Under an ATP system a computer will analyse the speed and braking pattern of a train and intervene if it anticipates a train is in danger," Mr Seabury said.

"If a driver doesn't slow down sufficiently when approaching a red signal, a lower speed limit zone or a work site, the train's brakes will automatically be applied."

Three companies were awarded contracts to participate in the trial period with each having to demonstrate their systems are inter-operable so RailCorp does not have to commit to one in the long term.

Testing will continue until May this year with a report to be prepared for the RailCorp board in mid-2008 so it can consider implementation of the technology.