AN INVESTIGATION into how a runaway trailer careered down a railway line in Cumbria last Sunday killing four track workers is focusing on its brakes.
'Trailers should be fail safe, ' said a Permanent Way Institution spokesman.
'Standard procedures and training should have avoided this incident. You've got to physically take the brake off to move the trailer.'
Network Rail has withdrawn all such trailers from use until they are found to be safe.
The accident happened on the West Coast Main Line at 6am last Sunday as contractor Carillion was carrying out maintenance work.
The trailer was being loaded with used rail at Carnforth South Junction near Shap when it began to roll.
It travelled 5.6km south before hitting the workers near Tebay and continued for another 800m before coming to a stop.
Four men were killed and three were injured.
The workers were operating under 'green zone' conditions when the track is closed to traffic, so no lookout was required.
Industry sources said sound of the trailer's approach would have been inaudible above the generators at the work site.
'The trailer left Shap, one of the highest points on the network, which enabled it to pick up quite a speed, ' said a Health & Safety spokesman at the scene.
A similar incident took place in January last year on the Settle to Carlisle line when an uncoupled trailer travelled 2.8km before coming to a halt.
The incident prompted the Railway Safety & Standards Board to order the installation of brakes on all trailers.
An HSE spokesman confirmed that the trailer in last week's accident did have brakes.