[globular-toast]

They don't always. There are self-driving trains operating full time in London and Paris as well as many other cities around the world. But they are low-speed trains operating at only around 30mph. High-speed trains run in excess of 180mph and heavy goods trains are often a mile long and weigh more than 10,000 tons. While much of the signalling is automatic these days, I think it will be a long time before we could think about running something so dangerous without a skilled human in the front ready to override the controls if necessary.