The Western Pacific had three automatic interlockings within CTC (the brand WP used was called "TCS") on the First Subdivision, at Elmhurst, Radum, and Lyoth (all crossings with SP lines). The dispatcher didn't control them, and they worked just like any intermediate signal unless they were red(of course, you didn't just stop-and-go since there might be a conflicting movement, and if there wasn't, you flagged them per the instructions in the release box). I always assumed they existed before TCS was installed, and that the WP was too cheap to replace them. In each case, the SP line being crossed didn't have much traffic.

Years later, I had a rules instructor say that it was "impossible to have an automatic interlocking within CTC." When I related that I knew of three located not far away, he just repeated that it was "impossible."