Moving cars!
June 15th, 2005 by RoscoHeadOK this isn’t new apparently, but I’ve never seen it done in LEGO before so it’s new to me 
The idea is to motorise vehicles on a town layout. The method has been pinched from model railroading, where this seems to be reasonably common. Basically, you stick a battery and motor in the vehicle, and metal wire or strips under the road around the path you want it to follow. Then you add a magnet that activates the steering, and voila!
So I’ve come up with a basic chassis, too big for a car, but should be OK for a truck or bus. I think to do a car, you’d need to use non-LEGO parts, probably commercially available internals. My chassis is all LEGO, 7 studs wide, and length is easily adjustable. Vehicle must be long enough for a battery box, plus a couple of studs for the drive and about 6 studs for the steering.
The next thing to think about is stopping at level crossings. In scale layouts this is achieved using an electromagnet under the road which activates a reed switch cutoff in the vehicle. That will be difficult with LEGO, but we may try it eventually. For now I guess they’ll just go round & round.
Anyway I’ll let you know how it goes.