Tracks used for professional speedway racing are regulated by the Fédération Internationale de Motocyclisme (FIM) who provide rules concerning construction, size and safety requirements. Speedway racing takes place on a level oval track consisting of two straights joined by two semicircles. Tracks must be between 260 and 425 metres (853 and 1394 ft) in length, this is measured at a distance of from the inner boundary. Tracks may be banked, but the gradient must under no circumstances exceed 5% in the straight, 10% in the bends, and must remain constant and grow from the inner edge to the safety fence. A white start line is marked across the track approximately mid-way along one of the straights. The starting area is also divided into four equal parts (known as gates) by white lines marked at right angles to the start line and extending back at least . Additional rules govern the placement of warning systems such as lights and also the construction of the starting mechanism. The minimum track width is on the straights and the bends must be at least wide. The minimum widths give each rider adequate space to safely navigate the track. The start line and starting gate assembly is halfway along one of the two straight sections of the track. Starting gates are simple spring-loaded mechanisms that raise two or three strands of tape to start the race.