Actually Ray, I had thought about using a rotating disc with magnets mounted to it on corners to transfer people from one belt to another. Then you would have the belts with the magnets mounted on it only run the length of the block and then roll back under, somewhat like an escalator. With the rotating discs on each corner the people would be transfered from one belt to another.
The problems that I see with them crossing the street are having a magnet strong enough to effect them through the thickness of the track, which would be thicker than the cardboard sidewalks. Also having some sort of insulation under the base so that it doesn't short out the slot track. The right lane wouldn't be a problem as it would be shut down to prevent cars from entering the intersection, but the left lane would remain live to ensure that any cars in the intersection had exited it before the light changed.
I hadn't really thought of tin, as I wasn't sure it was ferrous enough for magnets to effect it. With the tin painted the same color as the sidewalks it wouldn't be so obvious as to how they were moving. I think that a steady speed motor would work better than a stepper. Wouldn't that make their movements jerky?
I bought a bunch of small rare earth magnets that are very small but very powerful. They would attach to a belt, or even be encased inside it, and be great for the job. I had originally bought them to mount in the cars because the reed switches that I had bought weren't sensitive enough for the car magnets to activate. But then I found that one of the tiny magnets placed under the track moved when a car went over it, so all I have to do is affix it to a switch contact and the sensor problem will be solved.
If this works as well as I think it will, it will be a sight to see. Trains going by, cars zipping down the highway and pedestrians walking he street.