Four rail workers were killed by a runaway wagon in Cumbria after its brakes were irresponsibly dismantled to save cash, a court has heard.
The trailer rolled down the track before hitting the workers
The men were working on tracks in Tebay in February 2004 when the three-tonne wagon with 16 tonnes of steel hit them.
Mark Connolly, 44, from Anglesey, North Wales, and Roy Kennett, 28, from Maidstone, Kent, face four counts of manslaughter, which they deny.
The trial at Newcastle Crown Court is expected to last up to eight weeks.
Mr Connolly also denies three counts of breaching Health and Safety laws, and Mr Kennett denies one count.
Colin Buckley, 49, of Carnforth, Lancashire; Darren Burgess, 30, also of Carnforth; Chris Waters, 53, of Morecambe, Lancashire; and Gary Tindall, 46, of Tebay, all died while working on a section of the West Coast Main Line.
Noise from an on-site generator meant the group had no warning and the runaway wagon crashed into them at about 40mph.
Their families, in court on Tuesday, broke down in tears on hearing how the men suffered massive injuries, including loss of limbs.
The court heard that sub-contractor Mr Connolly was the boss of MAC Machinery Services and has been employed to replace and upgrade the rail network.
On the morning of 15 February, employee Mr Kennett was using a crane to lift ageing track from the line onto two wagons.
The court heard he had placed wooden "chocks" under the wheels of the wagons to ensure they did not move.
But as he unloaded the second wagon it began to roll down the track.
Robert Smith QC, prosecuting, told the jury Mr Connolly had deliberately disconnected the brakes on the wagons because the hydraulic systems were in such a bad way they would not work properly in conjunction with the crane.
Mr Smith said: "Instead of repairing the trucks and the crane, he devised the simple but grossly irresponsible and dangerously expedient practice of dismantling these brakes."
Mr Connolly then filled the cables connecting the wagons to the crane - usually full of hydraulic brake fluid - with ball bearings, giving the impression that everything was above board, the court heard.
Mr Smith accused Mr Kennett of failing in his duties because he knew Mr Connolly had dismantled the brakes.
But he continued to hide this from his supervisor Danny Jones by connecting the crane's faulty hydraulic braking system to the two wagons, the court heard.
Mr Smith said: "Roy Kennett, say the prosecution, knew what Mark Connolly had done to the brakes because he confessed to another member of staff that a ball bearing had been placed in the hydraulics."
The trial was adjourned until Wednesday.