Amey and Alstom have won work on the upgrade of the Great Western Main Line.
Network Rail awartded Alstom a £79M contract for the final stage of the signalling system that will control trains between Reading and Paddington.
Amey secured an £11M deal to deliver resilient power supplies between Paddington and Hayes & Harlington.
Both packages – awarded through existing frameworks – will also benefit Elizabeth Line services when the Crossrail project is completed.
Network Rail Crossrail programme director Matthew Steele said: “This is a vital step in the delivery of a bigger, better, more reliable railway for London and the South East.
“By ensuring the new trains can run seamlessly among existing rail services, and by building in resilience at the outset, we increase the capacity and reliability of the railway, meaning that passengers benefit from quicker and easier journeys they can depend upon.”