Network Rail said the Flying Banana, which covers 115,000 miles (185,075 km) of track, is "vital to keeping the railway safe and reliable".
The train, which travels at speeds up to 125mph (201 km/h), records track conditions and identifies faults before they can pose a risk.
To do this, it uses specialist equipment, such as a track‑geometry system, laser track scanners and a high‑resolution video camera.
According to Network Rail, by monitoring the tracks in this way, it avoids blocking railway lines and saves the company millions of pounds.
The nickname appears to be a playful take on the famous Flying Scotsman.