I've seen some very old-school electric 'pushers' people have fabbed up... imagine a small electric motor turning a small rubber wheel that is touching either the ground near the normal rear wheels or touching one of the rear wheels (in a reverse direction). All it does is creep the car along, then a lever disengages it when its time to burn some gas.
It seems like a really fun project, but a lot of to-do for traffic jams.
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