Stock car racing is a form of automobile racing foun mainly in the United States, Canada and Great Britain held largely on oval rings of between approximately a quarter-mile and 2.66 miles (about 0.4 to 4.2 kilometres) in length, but also raced occasionally on road courses. Ovals shorter than one mile (1.6 km) are called short tracks; unpaved short tracks are called dirt tracks; longer ovals are typically known as superspeedways. Top level races are generally 200 to 600 miles (300-1000 km) in total length. Average speeds in the top classes are around 160 mph (275.5 km/h), compared to 220 mph (354 km/h) in comparable levels of open wheel racing. Some NASCAR races can reach speeds of 204-208 mph (328-334 km/h) at tracks such as Indianapolis Motor Speedway and Lowe's Motor Speedway. NASCAR has implemented the use of restrictor plates at Daytona International Speedway and Talladega Superspeedway for safety reasons thereby limiting top speeds to approximately 187 mph (301 km/h) when not drafting.