Located at
Holloman Air Force Base, the Holloman test track is the fastest in the world. The track is operated by the
846th Test Squadron, the first test at the track was performed
June 23, 1950 and the test vehicle reached a scorching 150 feet per second (about 100 miles per hour).
In 1982, the track set the world land speed record with a 6,122 mph run, a record that still stands.
The track has been expanded many times since its inception and is currently almost 10 miles is length.
General Atomics is currently considering modifiying the track to a maglev system with a superconducting Halbach array using superconducting wire from the defunct Superconducting Super Collider program.
Sources:
http://www.aip.org/tip/INPHFA/vol-4/iss-4/p12.pdf
http://www.af.mil/news/Jul2000/n20000721_001101.html