being replaced but those under the down line being left alone. A further operation was scheduled for Easter 2002 to perform these final replacements. A roof collapse occurred in October 2009, necessitating the closure of the line for relining work. Accidents A collision took place near Sapperton Tunnel (mis-spelt as "Salperton") on 4 December 1851. A goods train approaching the tunnel from the Swindon direction was overcome by the gradient after passing Tetbury Road station, and the driver decided to divide the train, taking the front portion forward and returning later to collect the rear portion. Unfortunately the brakes on the rear portion failed and it ran back down the gradient to collide with a following train. The goods vehicles were destroyed and the driver and passengers of the following train sustained injuries, but there were no fatalities. A minor accident occurred at the tunnel on 29 October 1855 also involving a train becoming divided and one portion running away. There were no injuries or deaths and it is thought that no investigation was carried out. Four platelayers were killed in the tunnel on 14 April 1896. This is mentioned in Hansard for 27 April 1896 (the report mis-spells "Stroud" as "Strood") but no details are given. On 9 December 2009 a door on an HST came open in the vicinity of the tunnel and a passenger attempted to close it, without success but at some personal risk. A local newspaper attempted to sensationalise the incident by stating that the passenger concerned was "almost thrown from the train" as the door "flew" open. In fact nobody was near the door when it opened, and any risk to the passenger concerned arose entirely as a result of his decision to attempt to close it. Local councillor Andrew Gravells is quoted as saying that trains should be fitted with devices to prevent departure from stations if doors are open. This requirement already exists, and older slam-door stock such as the HST was retrofitted with a central door locking system in which a power-operated bolt, activated by the guard, prevents the doors from opening while the train is in motion; however this system is not interlocked with the driving controls. It is not clear how the system failed on this occasion; the RAIB was informed of the incident but no report appears to exist on their website. Disruption to train services was caused