British Transport Police (BTP) is appealing for witnesses to come forward after a lineside fire between Goldthorpe and Thurnscoe stations last week.
The incident, which took place in the late evening of Thursday, 21 July 2011 involved vandals accessing the line and setting fire to plastic piping.
Detective Constable Mick Kelly said: “Officers attended the incident, which was reported at 11.05pm, alongside colleagues from South Yorkshire Police and South Yorkshire Fire and Rescue Service and discovered that some plastic tubing had been set on fire.
“Fire crews extinguished the fire, which had spread across the wooded area – around 30 yards – reaching a relay box and causing signal failure.
“We are treating this incident as suspicious and have launched an investigation to find out those responsible for this reckless act.”
Officers have conducted several enquiries into the incident, including visiting local scrap yards, speaking to the local community and analysing forensics at the scene.
Two youths were seen in a cul-de-sac close to the scene of the crime, in Lindley Crescent, shortly after the fire was reported to police. The boys were later picked up by a group in a vehicle, believed to be a silver Toyota Corolla Verso.
Anyone with information about the incident, or of those seen those to the scene, is asked to contact British Transport Police on 0800 40 50 40 quoting background reference B5/NEA of 26/07/2011. Or call the independent charity, Crimestoppers, on 0800 555 111.