A plan to extend Crossrail to Hertfordshire is being considered by the government.
The line would take pressure off Euston during the construction of HS2, as well as providing economic benefits to the north-west of London.
Transport Secretary Patrick McLoughlin is expected to outline the proposal at the Farringdon Crossrail site in central London later today.
The Hertfordshire link would take Crossrail services to stations including Tring, Hemel Hempstead, Watford Junction, Berkhamsted and Harrow & Wealdstone.
Details of the proposed route have not yet been confirmed, but it is expected the line would branch off from the current Crossrail route near Old Oak Common, and then connect with the West Coast Main Line.
McLoughlin will say: “As part of our ambitious plans to modernise the transport network, I can announce today that we are looking at proposals to extend Crossrail services even further by opening a new route to key destinations in Hertfordshire.
“The plan would provide flexibility and reliability while we build HS2 into Euston.
“It would make it easier to get on with the massive job of rebuilding the station so it matches the standard of King’s Cross and St Pancras – because everyone who uses Euston now knows it isn’t up to scratch, and it would be a huge boost to Crossrail and London commuters.
“We’re going to examine, right away, how we can run extra services direct into the city and through to Canary Wharf from key stations like Tring, Hemel Hempstead, Harrow and Watford – without the frustrating need to change at Euston.”
HS2 Limited is now being asked to work closely with Crossrail to explore the plans in more detail.
According to McLoughlin, preliminary analysis has indicated that the link could potentially reduce journey times from Hertfordshire into central London by up to 15 minutes.