Buses are the dirty secret of the sustainability movement. While there is broad consensus that increased use of public transit is a Good Thing, self-powered buses -- the most flexible available form of public transportation -- are often noisy, pollution-spewing monstrosities. This is largely due to their diesel engines, a necessity due to the sheer power needed to push a massive vehicle along.
Now take a look at the current crop of hybrid-electric cars roaming the highways, such as the Prius or (the one I drive) the Honda Civic Hybrid. Quiet, efficient, clean... but they're no muscle cars. Surely there's no way to mix the two -- the power and utility of the urban bus and the quiet efficiency of the hybrid.
The city of Apeldoorn, in Holland, is about to start testing a bus design which is at least 50 percent more efficient than previous models. The bus will rely on a standard engine charging batteries supplying power to direct-drive electric motors in the wheels. It still runs on diesel (but will produce only a fraction of current model emissions), and from the perspective of both drivers and passengers the only notable difference will be how quiet it is. It will be the first real hybrid-electric passenger bus.
The company producing the wheel-motor system, e-Traction, claims that their innovation comes from taking a new look at traditional motors. Rather than a static ring of electromagnets making a rotor turn, the center bar is held still while the ring spins. This produces enough torque to push a bus. While regenerative braking is used to help recharge the batteries, most of the battery power comes from the diesel engine. But because the engine doesn't need to change gears or rev up and down as the bus moves, it can be run at its most fuel-efficient speed at all times.
The result is a vehicle which uses less fuel (but doesn't require an entirely new fuel infrastructure to be useful), produces far fewer emissions (without simply displacing emissions to the central electric power generation grid), and makes the experience of using public transit less unpleasant. Works for me.