i don't think driver implies an engine...

wagons were 'driven' by teamsters, (not drivers) but there are drover's who drove (lead the way and directed) cattle (and other live stock) to market.

you can drive a car (engine) or be driven crazy (no engine!)
you can be a designated driver or replace the print driver software.

you can drive home a point, or take long drive off a short pier...
a driver can be a person, a piece of hardware or a software, or part of an idiom. (great thread!)

my other obsession