London Underground, Tube Lines Ltd and Schweerbau GMBH had pleaded guilty to endangering passengers and staff under Health and Safety law, after the 39-tonne maintenance wagon hurtled through seven stations before it could be stopped.
A train in front of it was told to keep going and not stop, while its passengers were told to run to the front carriages, the Old Bailey heard.
Judge Richard Hone said: "There was the potential of terrible tragedy."
He said the runaway train was out of control for four miles during 16 minutes.
"To those involved it must have seemed an extremely frightening eternity," he added.
More top news
If you're dreading going to work Monday morning, how about this for a career change.
Police have released more images of people wanted in connection with what they describe as 'disorder' at a McDonalds in central London.
Four teenage girls, one of them aged 15, have been arrested following what police are describing as "disorder" at a McDonalds branch.