Like other electric vehicles, trolleybuses are often seen as more environmentally friendly than fossil fuel or hydrocarbon-based vehicles (gasoline, diesel, alcohol, etc.), but the power is not “free”, having instead to be produced at centralised power plants, with attendant transmission losses. On the other hand, centrally-produced power has the advantage of being more efficient, not bound to a specific fuel source and more amenable to pollution-control as a single-source supply than are individual vehicles with their own engines that exhaust noxious gases and particulates at street level. Moreover, some cities, like Calgary, Alberta, run their commuter light rail networks using wind energy, which is effectively emission-free once the turbines are built and installed. A further advantage of trolleybuses is that they can generate electric power from kinetic energy whilst braking, a process known as regenerative braking.