Decades before automated metro lines or autonomous vehicles made headlines, London was quietly operating a driverless electric railway beneath its bustling streets. Opened in 1927 by the General Post Office, the Post Office Railway—later known simply as Mail Rail—was designed to solve a very 1920s problem: London's notoriously toxic pea-souper fogs and congested surface traffic were crippling citywide mail deliveries. The solution was radical: build a dedicated 6.
5-mile narrow-gauge underground network running 70 feet below ground, connecting major sorting offices from Paddington in the west to Whitechapel in the east. What made Mail Rail truly revolutionary was its driverless automation. Engineers devised an ingenious electromechanical system using track circuits and switchboards.
Dispatchers controlled the uncrewed train cars remotely from station control rooms. Power was applied to or cut from specific track sections to move, stop, or hold trains automatically. Reaching speeds up to 35 mph, these driverless trains zipped through narrow 9-foot diameter tunnels, moving up to four million letters every single day at its peak.
The system was so reliable that during World War II, parts of the tunnel network were even used to safely store priceless treasures from the British Museum, including the Rosetta Stone, protected from Blitz bombings. Mail Rail operated continuously for 76 years until high operational costs led to its closure in 2003. Today, a preserved section of this forgotten automated marvel allows visitors to ride the historic subterranean routes.