Since Monday (7 February), new trains that cut noise by 70% and pollution by 90% have been operating between the Aylesbury and London Marylebone stations.
Chiltern Railways has named the service, which will significantly cut CO2 emissions, save fuel and reduce noise and air pollution, HybridFLEX.
Currently, the two-carriage trains have been rolled out on the commuter service between Aylesbury and London Marylebone only.
It's the first UK train of its kind that can reach a speed of 100pmh and is ran on battery and diesel power.
A spokesman for Porterbrook who owns the new train, said: "The train has been retrofitted with a Rolls-Royce powerpack which means quieter and quicker journeys and a 25 percent reduction in CO2 emissions on every journey.
"Nitrogen oxide and pollutants are also cut by 70 and 90 per cent respectively.
"The HybridFlex train substantially cuts fuel usage and reduces noise by up to 75 per cent in and around stations and urban areas."
Rolls-Royce also played a role in converting the diesel trains to make them more efficient and environmentally responsible.
Richard Allan, Chiltern Railway’s managing director, said:“Chiltern Railways is determined to operate a railway that is as sustainable and environmentally friendly as possible.
“We have worked hard with our partners to fit a powerful battery power pack underneath a 20-year old diesel train to make the train cleaner, quieter and quicker.
“We are really proud that this concept train is now carrying customers and look forward to assessing its performance in daily service.”
Plans are in place to bring the new type of train to the London to Oxford via Bicester Village route in the coming months.
Mary Grant, CEO of Porterbrook said: “The entry of our hybrid battery-diesel train HybridFLEX into passenger service is great news for Chiltern Railways and its customers.
"It’s a significant first step in demonstrating how improvements to this fleet can reduce emissions and improve air quality both at stations and other locations across the network.
“HybridFLEX is part of Porterbrook’s growing portfolio of alternative traction systems designed to help deliver a more sustainable railway.”
Warren East, CEO, Rolls-Royce added: “In this critical decade of climate action, today’s entry into service of the HybridFlex train demonstrates what we can achieve through technological innovation and agile collaboration.
"This smart piece of engineering enables the acceleration of the UK Government ambition to remove all diesel-only trains from the network by 2040, making rail journeys quieter, cleaner and faster.
"We’re delighted to be part of this groundbreaking team alongside Porterbrook and Chiltern Railways and look forward to seeing the train in service.”