The longest are the 2008 Victoria line replacements at 440 feet, 8 ft 8 inches wide and 9 foot 4 inches tall. They are produced by a Canadian company called Bombardier in the US state of Vermont...
Started construction in 1855.
Train.
Electric traction motors in each car via a "3rd rail" feeding electricity.
All of the current underground trains are powered by electricity, using a third rail. When originally built, the trains were coal-fired steam trains.