Diesel trains currently operate on the First Great Western service
Transport Secretary Lord Adonis has announced plans to electrify a rail route through Oxfordshire as part of a £1bn investment in the rail network.
He said electric trains were greener, more reliable and cheaper to run.
The Didcot Parkway to Oxford branch route is due to be electrified within the next eight years.
The London to Swansea and Liverpool to Manchester main line routes will also be electrified. Passenger group Ox Rail Action said it welcomed the news.
Group spokesperson, Zahra Akkerhuys, said: "It's a step in the right direction for the future of train travel, but as a commuter we've got questions about how long this is going to take."
Ox Rail Action was formed in 2007 in response to frequent delays and cancellations on First Great Western's Oxford to London route.
Mrs Akkerhuys said the train company had responded well to the previous concerns of its 150 members but she was concerned Network Rail did not "have a good track record" of completing projects on time.
Lord Adonis: "With electric you get a quieter, cleaner, more reliable and much cheaper train"
She said the group would be "deeply concerned" about the potential disruption along the whole line during the three planned phases of engineering work.
The announcement on Thursday came five days after Network Rail began six weeks of engineering work on the Oxford to Worcester line, in preparation for laying a second track along the route by 2011.
Network Rail said it had an "enviable record" for delivering big engineering projects and its £9bn West Coast main line upgrade - the biggest civil engineering project in Europe - was completed on time and within budget.
Mrs Akkerhuys said passengers would also want to be reassured the project was not going to lead to spiralling costs and increases in the cost of travel.
Lord Adonis told the BBC the £1bn investment would pay for itself over a 40-year period and there would be no impact on fares.
Electric trains do not carry their own fuel and also have lighter engines, which makes them 35% cheaper to operate than diesel trains, the Department for Transport said. Electric engines also require less maintenance and are around 20% cheaper to buy, it added.
Network Rail said: "Our plans for electrification revolve around state-of-the-art mobile factory trains which will allow us to drastically cut the time it currently takes to install overhead power lines.
"The overwhelming majority of this work will be carried out overnight with no impact on passengers."
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