A Dubai-based company called Fleethorse has designed several horse-powered vehicles, including the NaturBus above. The range is powered by horses running on a treadmill, supplemented with electric motors, and they claim that it's the greenest transportation possible. I really hope that this is a hoax.
The conveyor belt apparently starts to move, which encourages the horses to start walking. That walking movement is then harnessed to power the vehicle. The electric motors would be used when going up hill in order to avoid any undue strain on the animals. The waste product is of course, excrement, which is collected at the back of the belt as it drops off. Have a look after the link for the weirdest marketing video you are ever likely to see.
The problem is though, that horses aren't convenient enough to use as a power source. They require a huge amount of looking after. If you have to keep two or three horses in order to power your vehicle, then you may as well just ride one of the horses - it's more efficient, you don't have to buy an expensive vehicle and it's probably more fun for you and the horse. ::Fleethorse via ::Auto Blog Green