GAMBAR MOBIL DRAG:Before each drag race (also known as a pass), each driver is allowed to perform a burnout (which heats the tires and lays rubber down at the beginning of the track, improving traction). Each driver then lines up (or stages) at the starting line. Informal drag races can be started by any means, including flag-waving and arm-dropping. These methods are more likely to be seen in an un-professional setting, being most popular with illegal street racing. Professional sanctioned drag races are started electronically, with a series of vertically-arranged lights known as a "Christmas tree" or just "tree". A "Christmas tree" consists of a column of lights for each driver/lane. In each column, the top two lights are small amber lights connected to light beams on the track, which when broken by the vehicle's front tires indicate that the driver has pre-staged (approximately 7 inches (180 mm) from the starting line) and then staged (at the starting line).