I think there are a number of ways of achieving this but it’s fundamentally important to ensure that whatever you choose is reliable. A basic solution which relies on direct electrical contact is probably the least reliable as contacts can get dirty or fail.

Two simple switching solutions spring to mind (but I’m sure there are others), one requiring more extensive modification to the turntable than the other:

1. Microswitches with some form of arrangement whereby the turntable bridge closes the switch when it is aligned with that particular road. You’d need one switch per road and would have to drill through the wall of the turntable well so that the switch protruded through sufficiently for something on the turntable bridge to touch it and close the switch.

2. Reed switches. These would just need gluing onto the outside of the turntable well with magnets at either end of the bridge. Again, you’d have one switch per road (which would be closed by the magnet when the bridge was aligned with that particular road) and, apart from attaching the magnets to the bridge, no modification to the turntable would be needed.

You could also look at using an Arduino using hall effect sensors and magnets to know where the bridge is and relays to switch the individual roads on and off. It’s a far more complex solution of course but if you enjoy tinkering with this sort of thing, great fun.

Whichever solution you choose, there’ll inevitably be a bit of experimentation needed but that’s part of the fun of this hobby.

Good luck!