Proposals to extend Crossrail to Hertfordshire are being considered by the government, Transport Secretary Patrick McLoughlin has announced.
Extending the service would reduce journey times between London and parts of Hertfordshire by up to 16 minutes.
At Crossrail's Farringdon site in central London, Mr McLoughlin said the plans would also provide an opportunity to redevelop Euston station.
Business groups in the area said an extension would drive economic growth.
Mr McLoughlin said the proposals would take the pressure off the Tube's busiest sections and make it easier to improve Euston - which will have 11 new platforms built under proposals for the HS2 high-speed rail project between London and the West Midlands - because it currently "isn't up to scratch".
Under the plans, the current Crossrail project would be extended through north west London to stations including Tring, Hemel Hempstead, Watford Junction, Berkhamsted and Harrow and Wealdstone.
Addressing Crossrail workers at Farringdon, Mr McLoughlin said: "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.
"I have made clear to my department that any changes must not affect the timetable or planned service pattern for the existing Crossrail scheme.
"Final decisions would be subject to a wide range of considerations, including affordability," he said.
The £14.8bn project is scheduled to be fully operational by 2019.
Journey times if Crossrail extended:
•Tring to Liverpool Street - 57 minutes (a reduction of 13 minutes)
•Watford Junction to Canary Wharf - 43 minutes (a reduction of 12 minutes)
•Tring to Bond Street - 55 minutes - (a reduction of 16 minutes)
•Watford Junction to Liverpool Street - 37 minutes (a reduction of 13 minutes)
Source: Department for Transport
London Mayor Boris Johnson backed the proposals, saying: "I have always maintained that the renaissance of Euston is a fantastic opportunity for regeneration in our city and one we should not miss.
"Providing a new rail route into the capital for passengers from Hertfordshire will be vital for Euston to be properly redeveloped to accommodate HS2 and to maximise the delivery of new homes and jobs in London and beyond."
Yolanda Rugg, chief executive officer at the Hertfordshire Chamber of Commerce, said including Hertfordshire in the scheme would be "a catalyst to drive economic growth" in the area.
"It will provide vital high-speed transport connectivity from London to the new Watford Health Campus, and to the financial and creative services sectors," she said.
"It will most definitely support long-term regeneration across Hertfordshire."
David Perry, leader of Harrow Council said new investment in London's infrastructure was "welcome, along with the potential regeneration opportunities this will bring to Harrow".
The Crossrail project is the first complete new underground line in London since the Victoria line was built in the late 1960s. The first stage is due to open in 2018.
Trains on the line will run from Reading in Berkshire to the west of the capital and as far east as Shenfield in Essex, as well as linking to south London.
The latest development comes days after Chancellor George Osborne pledged his support for a "Crossrail of the North" plan.
Representatives from Leeds, Liverpool, Manchester, Newcastle and Sheffield are calling for a £15bn 15-year plan to be adopted to improve transport.
The One North report says a 125mph trans-Pennine rail link, a faster link to Newcastle and better access to Manchester Airport are needed.