Here's a little info about the Milwaukee-Soo interlocking in Burlington WI. It was originally manned by an operator until the 1960s(?) when control was transferred to the Soo dispatcher in Stevens Point. My father and his siblings frequented the interlocking as kids and kept the operators company. In fact, one of the operators (in the early 1950s) met my father's sister and eventually married.
The Soo had searchlights on each side of the interlocking with two heads each. The aspects were Clear, Approach, and Stop. There was also a restricting (Red over yellow) aspect that could be used to allow a train/engine through the interlocking into an occupied block. The Soo was CTC in this area and this interlocking tied into the signal system.
The Milwaukee had colorlights capable of clear and stop aspects. Distant signals were placed in both approaches and could show clear (the interlocking was lined for a Milwaukee Road train) or approach (the interlocking is NOT lined for a Milwaukee Road train and any Milwaukee Road train should be prepared to stop short of the interlocking limits).
