The lan speed record is the fastest speed achieved by any wheeled vehicle on land, as opposed to one on water or in the air or on rails. It is standardized as the speed over a course of fixed length, averaged over two runs in opposite directions. The current absolute (or unlimited) record holder is ThrustSSC, a twin turbofan jet-powered car which has achieved 763 mph (slightly under 1228 km/h) over one mile (1.6 km), breaking the sound barrier. There are also records for specific classes of vehicle, such as motorcycles (350.884 mph/564.69 km/h, currently held by Chris Carr), and steam-driven vehicles (Fred Marriott, 127.659 mph/205.45 km/h), but this list only includes the absolute speed records for wheeled vehicles on ground, without rails. Early records predate standardisation and are sometimes controversial.