Train disruption during Swindon signal upgrade
Network Rail has begun testing a major signalling upgrade on the Great Western main line in Wiltshire.
The new system will replace equipment installed in the 1960s and 70s.
A 20 mile stretch of the line has been closed, in preparation for control of the railway to move from the signal box at Swindon to the Thames Valley signalling centre in Didcot.
Services from south Wales, the west and south west will be diverted during the temporary weekend closure.
Paddy Gregg, Network Rail's signalling project director, said: "We are now entering the vital, more technical stages of testing the new signalling system."
He added: "Testing new signalling equipment is very complex and for safety reasons must be carried out when trains aren't running."