En route to a new icon

There can't be many automotive icons more evocative than the London double-decker bus — or, to be more specific, the Routemaster with its goggly headlights, distinctive radiator grille and rounded contours. And, most of all, that open rear platform with the pole on the corner, allowing passengers to jump on and off whenever they wanted.

But, of course, the Routemaster is no more. Former London mayor Ken Livingstone signed its death-warrant when he brought in the continental-style bendy buses, loathed by many for their bulk and ability to block London's narrow and oddly-angled road junctions.

They may be more accessible to wheelchair and pushchair-users and offer more knee-room than the Routemaster, but they sacrificed the convenience of the open platform for the greater safety of doors. A few old Routemasters still ply a couple of tourist routes, providing photo opportunities as they round Trafalgar Square or glide over Westminster Bridge, but mostly their days are past.

Or they were, until new mayor Boris Johnson, the Conservative with an eye for the populist gesture, made it part of his electoral campaign platform to bring back the bus with the platform. After winning the election, he launched a competition to design a new Routemaster, with a prize of £25,000. Well over 400 entries later, the competition is now closed, and a winner is expected around the time you are holding this issue of The Engineer in your hands.

But there are winning designs, and then there are designs that get built. Transport for London (TfL) the body which will oversee the ordering and deployment of any new buses, declined to be interviewed for this feature. However, its programme manager for new buses, David Hampson-Ghani, has been reported as saying that the company which wins the manufacturing tender for the new-generation Routemaster will be handed a folder of the winning designs and asked to come up with their own fusion of the best concepts, features and technological fixes.

So, looking at some of the designs from higher-profile entrants, what sort of features could London's next public transport icon have?

The stipulations of the competition were rather sketchy. The new design had to have an open platform, good use of interior space, and it had to be accessible; it also had to use green technology in some way. Apart from those, the page was blank.

One new Routemaster design actually pre-dated the competition. Last Christmas, Autocar magazine commissioned Capoco Design to come up with a concept for a hi-tech but retro double-decker. Capoco's creative director, Alan Ponsford, said that the company had entered the mayor's competition with an amended design, but its original includes some interesting features.

Chief among these is the drivetrain. The bus still has an engine up front, behind a very familiar-looking radiator grille, but it doesn't drive the wheels and it isn't diesel. Instead, Ponsford opted for a 2.3 litre Ford petrol engine adapted to burn hydrogen, similar to one that Boeing is currently using to drive a UAV drone, with the fuel stored in a filament-wound tank below the bus's staircase.

This engine runs at a constant, optimised speed, turning a 97kW generator that charges lithium ion batteries. These are mounted in front of the rear axle alongside electric motors which drive the rear wheels.

This eliminates the gearbox, propshaft and rear differential, and increases the usable floorspace on the lower deck, while also allowing it to be mounted low, below the centre-line of the wheels. It also improves the environmental performance of the bus: even if the engine were hydrocarbon-fuelled, running it at a constant rate removes the pollution associated with the constant inefficient stop-start and slow crawl that bus travel requires.

In Capoco's design, the bus is built around an extruded aluminium spaceframe, lighter and stiffer than the welded steel used in most current buses and similar to the original Routemaster's. This is clad with rolled aluminium panels and floors made from bonded honeycomb sandwich sheets.

Capoco's engine concept is likely to be similar to the drivetrain used by the eventual design. The UK's largest bus-maker, Falkirk-based Alexander Dennis, which is certain to bid for any contract to build a new bus, has an 80-strong team working on hybrid bus drive technologies and has recently launched a hybrid model, the Enviro500.