Reply to "How to make a trolley stop on its own with k line streets"

You could also use a simple 555 timer circuit with a relay activated by a magnet on the trolley. The relay turns the isolated center rail on and off. A 555 timer chip costs forty eight cents. The other componants a few pennies, except for the relay and the reed switches. A variable resister enables you to set stop time from ten seconds to ten minutes.