Definition of "driverless"

Will Underground trains be completely driverless? The new signalling being installed as part of the Upgrade will allow this, and the development, allowing a faster throughput of trains, might arise from, or be stopped by, a battle with the unions. Mike Brown, Managing Director of London Underground, envisages driverless trains within twenty years.

2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, page 277

One of the latest [conditions], from last summer, was that Transport for London should look again at driverless trains. I examined their prospects in RAIL 933, and it's fair to say that their introduction is technically difficult and very expensive. If introducing driverless Tube trains were easy, then I'm quite sure that Prime Minister Boris Johnson would have brought them into service during his two terms as London mayor.

2021 December 1, Philip Haigh, “TfL's deepening financial crisis puts Tube services at risk”, in RAIL, number 945, page 59