London Mayor Sadiq Khan has unveiled the world’s first double-decker hydrogen bus, which will be trialed on the city’s roads in 2017.

The move is part of the mayor's effort to phase out the purchase of new pure-diesel buses for use in the British capital. Khan revealed that no more pure-diesel double-deck buses will be added to the city's fleet from 2018 and that all new single-decks for central London will be zero-emission.

Zero-emission transit vehicles, such as this hydrogen bus, have begun replacing pure-diesel buses in central London. Image credit: Wrightbus.Zero-emission transit vehicles, such as this hydrogen bus, have begun replacing pure-diesel buses in central London. Image credit: Wrightbus.The bus, manufactured by UK-based Wrightbus, carries a zero-emission drive system that encompasses a hydrogen fuel cell and a battery pack with management system to continuously monitor and balance the stored power while the vehicle is in service. It also incorporates an electric-drive axle situated to allow a full flat floor throughout the bus, a zero-emission heating/cooling system, the ability for overnight charging if the operator desires and remote diagnostics.

London has committed to procuring roughly 300 zero-emission buses by 2020. Recently, 51 battery electric buses were put into service, taking the total number of zero-emission buses in the city's fleet to 79.

“I want London to become a world leader in hydrogen and electric bus technology," Khan says. "I’m implementing hard-hitting measures to clean up London’s toxic air. It’s great that more cities are getting on board to phase out the procurement of pure-diesel buses, which sends a clear signal that only the cleanest technologies are wanted in our cities."

Eleven other major cities—including New York, Los Angeles, San Francisco, Amsterdam, Copenhagen and Cape Town—have likewise begun moves to phase out their procurement of pure-diesel buses by the end of 2020. In addition, Paris, Madrid and Mexico City have committed to removing diesel buses from their cities by 2025.

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