By Mark Brown, Wired UK

The first of London’s next-gen double-decker buses is a hybrid that officials promise is “most environmentally friendly” and “the latest, greatest masterpiece of British engineering.”

Please keep your Lucas jokes to yourself.

The bus, unveiled Friday in Trafalgar Square, is the first designed specifically for London in more than 50 years. The Routemaster-inspired bus went from the drawing board to a fully functioning prototype in just two years. Transport for London awarded the contract for engineering design to Northern Ireland-based Wrightbus in January 2010. Wrightbus and London’s Heatherwick Studio have now finished the first prototype.

The shiny red bus has three entrances and two staircases to speed up boarding. There are huge windows that snake up alongside the stairs to increase the amount of light let in, an open platform at the rear and even a new seat design and fresh upholstery.

Transport for London claims the hybrid double-decker bus “will be the most environmentally friendly bus of its kind when it enters passenger service.” The engineering test vehicle uses a hybrid drivetrain developed by Volvo. It emits 640 grams of CO₂ per kilometer — less than half of that of current diesel buses (1295 g/km). In testing, fuel economy was also better than twice that of a standard diesel bus, clocking in at 11.6 mpg.

“It is the latest, greatest masterpiece of British engineering and design, and I am certain it will become a much-loved and iconic vehicle akin to the legendary Routemaster from which it draws so much inspiration,” said London Mayor Boris Johnson, who called for the new bus during his election campaign.

He also announced that the first bus, operated by Arriva, will begin carrying passengers on the busy Route 38 (Victoria station to Hackney) on Feb. 20.

Still, there was a spot of bother for hizzoner and Transport for London earlier today when the bus conked out on the highway.

According to the Evening Standard, the bus ran out of juice on the M1 motorway. A spokesman for the transit agency said a battery warning light prompted the driver to pull to the shoulder and recharge. At that point, another warning light came on, so TfL decided to investigate further. Authorities summoned a tow truck, but it ultimately was not needed.

The transit agency said the bus’ battery was designed to recharge during stop-and-go city traffic, not during a long highway haul.

“When the bus undertakes long, non-stopping motorway journeys, such as its journey to Bedfordshire this morning, it can lose charge and the driver is briefed to pull to the side of the road to allow the battery to recharge,” Mike Weston, London Buses Operations director, told the Standard. “After the battery had re-charged the driver was unable to re-start the engine. It was later established that the bus had run out of diesel. Once the bus was refuelled it carried on its journey. We will be speaking with the operator to ensure that this does not happen again.”

Eight prototype buses will enter passenger service in the first half of 2012. If the trial is successful, hundreds of them could be running around London in the coming years.

Photo: Transport for London