vehicles are stripped of interior fixtures, trim, plastic, lights, and glass. They are repainted, often in loud, garish designs and on low budgets (spray paint is frequently used to mark names, slogans and identification). Additional modifications include trimming sheet metal from around the wheel wells, removing parts of bumpers, welding the doors shut, and relocating the battery and gas tank. The radiator is sometimes relocated to the back seat. To make the cars last longer, they are occasionally pre-bent, with frames notched, rear bumpers removed, trunk lids notched, and rear coil springs are (when rules allow) replaced with leaf springs. In many instances, roll bars, fire extinguishers, and other safety equipment is installed. Sometimes the removed parts create bulk availability of off-color parts for older cars that are compatible with them. In most cases, any vehicle parts must be "stock", though in some derbies a "gladiator" or "outlaw" division allows cars to be extensively modified and reinforced. Popularity In 2001, the Los Angeles Times estimated that between 150,000 and 225,000 drivers participated in at least one of the 2,000 demolition derbies held in the United States that year. Event purses rose from a pittance of a few hundred dollars to over $50,000 after the popularity of TNN's Motor Madness series. In 2017 one of the most popular Demolition Derby series is the Tour of Destruction which features School Bus Racing, Trailer Racing, Car Soccer and a large Demolition Derby. These events are viewed by up to 5000 spectators. Rules Derbies have many different sets of rules, often pertaining to how much welding can be done to the vehicle, and the class of car (example: compacts, trucks, minivans, full size; some rules are 1980 and newer, etc.). Drivers are often required to be at least 16 years old and hold a valid driver's license. They are required to have seat belt and a helmet, and, depending on sets of rules, roll over bars and cages inside the vehicle. An event usually begins with drivers lined up on the track facing rear to rear, or circling on an oval track. Drivers are usually required to crash into another vehicle every 2 minutes or they are labeled as "sandbagging" and become disqualified. Hitting a driver intentionally in the driver's door and sometimes rolling another car intentionally, are also grounds for disqualification. When a car is disabled or loses power, the driver is allowed