A 1.6-mile abandoned railway tunnel in the United Kingdom has been converted into a supercar test track.

Part of the former Great Central Main Line, the Catesby Tunnel will soon become a 24/7 testing facility for engineering firm Aero Research Partners (ARP), according to a New Civil Engineer article on the project. The facility opened to the public in November 2021, according to the Catesby Tunnel website, although the tunnel's owners haven't announced what companies might use the facility.

The tunnel was completed in 1897 and closed in 1966. It then sat abandoned for more than 50 years. After proposals to reopen it as a rail line fell through, approval was granted in 2017 to convert the tunnel into an aerodynamic testing facility for supercars and race cars. 

Part of that conversion involved racetrack-spec asphalt, including the same stone used to pave the Silverstone, Bahrain, and Abu Dhabi tracks that host Formula One Grands Prix.

The advantage of a tunnel test track is that it allows cars to be driven at significant speeds in an enclosed space that is unaffected by weather. That creates repeatable conditions, unlike outdoor testing where changes in weather can affect results. In addition to aerodynamic testing, the facility can be used to test cooling, noise, and emissions.

The idea isn't unprecedented. Pennsylvania's Laurel Hill Tunnel was used by Chip Ganassi Racing for aerodynamic testing of race cars beginning in the early 2000s. The 4,541-foot tunnel was built for a never-completed railway line, then became part of the Pennsylvania Turnpike before being bypassed. The converted tunnel was reportedly first used to test Indy Racing League (IRL) cars in 2004, with cars running at speeds up to 130 mph.