The Ehra-Lessien (sometimes simply 'Ehra') test track facility is located near Wolfsburg, Germany in the district Gifhorn, and is owned by Volkswagen Audi Group (VAG). It is located near to the headquarters of VAG.
The facility features a large variety of road surfaces and curves to test vehicles. More significantly, there is an unbroken straight of 9 km in length, on which the top speed of the very fastest of supercars may be determined.
This is where the Bugatti Veyron 16.4 hit a top speed of 253 mph (407 km/h)! Don't believe it? Check the link!