This article defines a "bus zombie" as a person who is almost, but not quite, asleep on public transport. The dazed fatigue state where the eyes are half closed and the person is technically awake, but really somewhere between there and asleep. That's been me more often than I care to admit.
Mokalus of Borg
PS - An interesting image.
PPS - It's a good thing they don't want brains.