First impression...  it's cramped in here, there isn't enough room to turn around even if one tries, and I'm sitting very close to complete strangers shortly after the COVID-19 pandemic. If you're claustrophobic, RUN AWAY, you don't ever want to ride in one of these contraptions.

So, what is Mail Rail? The Royal Mail Postal Museum is located on Phoenix Place in London, England. Just across the street is the entrance to Mail Rail, now part of the Museum. Mail Rail's terminal is located underground below this building. Mail Rail is comprised of small automated trains which run on narrow gauge tracks in underground tunnels. Once part of the original underground Post Office Railway that was previously used to distribute sacks of mail between several points in London. Part of the original line is now a tourist attraction the public can ride to explore the tunnels, view animated clips describing the history of the railway projected onto the tunnel walls at several station stops, and examine the unmanned locomotives used to haul the trains plus various other equipment.

This 2 foot gauge railway line is 6.5 miles end to end containing 23 miles of total trackage. Trains are powered by electric locomotives using 440 Volts DC through a third rail located between the running rails. The mainline lies in a single 9 foot diameter tunnel containing 2 tracks but prior to entering stations mainline tunnels split into 2 single track tunnels of 7 foot diameter. Each station contains 2 parallel tunnels 25 feet in diameter. Mainline tunnels average about 70 feet below the surface, however, stations were constructed at a shallower depth having a 5 percent gradient on each side of a station. This assists trains in slowing as they enter, and speeds them up on departure. Speed on the mainline is a surprising 40 mph with trains slowing to 7 mph through stations, platforms, and sidings. The current Mail Rail trains with passengers come no where near 40 mph, thankfully!