Signalling equipment along the Salisbury to Exeter railway line is to be modernised as part of a £20m scheme.
Network Rail said some of the infrastructure dated back to the 1960s and was coming to the end of its life.
The 90-mile (144km) route carries more than 40 trains a day and is fast becoming a vital link for businesses and communities, it said.
The upgrade is expected to improve the reliability of the system and extend its lifespan for another 35 years.
'Vital building blocks'
Richard O'Brien, Network Rail route director for Wessex, said: "The number of passengers travelling on the Salisbury to Exeter railway has been steadily rising and it is key that the railway remains robust and reliable to serve this burgeoning demand.
"We want the railway to continue to thrive and with this scheme, we will be able to set up the building blocks that are vital to protect the future of the railway so that we can continue to serve even more passengers for many years to come."
Major level crossings along the route are also to be upgraded to improve safety.
Work will be carried out from the beginning of autumn 2011 and it is due to be completed during 2012.