Great Western main line signalling scheme to begin
A £350m scheme to upgrade signalling on the Great Western main line is to begin later.
Network Rail said the improvements would benefit rail services through Bristol, Bath, Chippenham, Swindon, Didcot, Oxford and Newbury.
A spokesperson said the work was "essential" to prepare for expansion on the line and electrification.
The project has been paid for out of a Government settlement which had already been agreed.
Network Rail said the current system which controls the signals, known as interlocking, dates back to the 1960s.
A spokesperson said the project would effectively be a "brain transplant" with the old system being replaced by modern computers.
They said the four-year scheme, when finished, could "help cut delays on the line by 50%".
Patrick Hallgate, from Network Rail Western, said: "The line is running out of room with nearly 30m journeys and a growth rate of at least 5% each year.
"A robust and modernised signalling infrastructure is vital to cope with this burgeoning growth."
Last year the Government announced a £5bn investment programme of rail electrification and intercity service improvements on the Great Western rail route.