By John Thorne
BBC correspondent in Tebay
The signal on the up and down lines was on green and the site of the terrible Tebay accident had been cleared and fresh rails installed.
The accident happened where the train line, M6 and River Lune meet
The first inter-city express train sped past, heading south just after six on Monday morning.
Just 24 hours after the tragedy the West Coast Main Line was re-opened, as the joint police and Health and Safety investigation got into its stride.
The area, just south of the Cumbrian village of Tebay, is particularly picturesque - the rail line passing through the South Lakelands.
Where the maintenance gang of 10 men were working, the six-lane M6 motorway towers above on the east.
Below, to the west, the River Lune tumbles through the rocks as the three different communication systems fight for space along the meandering valley floor.
The investigators are trying to plot exactly what happened on one of the busiest rail networks in Britain.
What was the sequence of events? Was it human error?
Should the trolley carrying over 15 tons of 18ft long steel rail sections have been physically "parked" with wooden chocks on the line?
Darren Burgess, left, and Colin Buckley, died in the accident
Was it a mechanical fault? Did the flatbed wagon become detached from its engine when the coupling failed?
Or is there a systems failure in the way in which this sort of maintenance work is organised?
One railway man working on the West Coast line at the time of the incident is quoted as saying: "This was the worst nightmare of any rail man....an unmanned wagon coming straight at you out of the pitch darkness."
One of the four men who died lived in Tebay itself.
Garry Tindall was 46. He went to school in Tebay and he captained the social club darts team.
He was part of the fabric of the community and part of the fabric of the railways.
An investigation into the cause of the crash is underway
Mr Tindall's son Darren is also a railway worker.
According to the local Methodist minister, Phil Dew, the effects of the tragedy have shattered a village that has historical links with the rail network that skirts past.
Now with the line re-opened, despite union demands that all such maintenance work should be suspended, the investigation will focus on two avenues.
British Transport Police officers will seek full eye-witnesses accounts from the survivors and from their colleagues working four miles further north, who saw the runaway wagon start its lethal journey.
And Health and Safety Executive inspectors will begin to dismantle the maintenance rail wagon to discover whether something in its design or function helped to create the tragedy.