Controlling the flow of traffic

Caption: "Controlling the flow of traffic--The Bay Ridge Model Railroad [Club] has a signal system based on that used by the New York Central Railroad. ... Robert O. Kretzschmar of 8300 4th Ave., ... operates the signal system, premitting a freight to move safely through the switches. A diesel engine heads out of the tunnel and, at right, a passenger train rounds the bend, approaching a signal bridge on the mainline."