There were a couple of messages posted in July regarding photos in this new book. While looking at my newly arrived copy, I noticed another photo taken at Hinsdale, in the middle of page 173, that documents a little bit of signal history.
This photo is taken looking east from the west end the new Highlands remote control interlocking that was constructed (along with West Hinsdale) in 1954. It is probably one of the earliest photos of the 4 track signal bridge at MP 16.69. It had been installed new at MP 11.60 east of Hollywood in 1913, and was taken down in 1953 when signal respacing for cab signals was being progressed, and re-used here for the new control point.
Notice the 3rd (bottom) target on the Main 1 Eastward signal. It does not appear in later (i.e. 1960's) photos. But in 1954, Main 1 was still a Westward Main between Congress Park and Highlands, and trains running against the current ran under Manual Block System rules. A train running east on Main 1 from this location would get a Restricting signal aspect, which for this location needed to be RED over RED over YELLOW, per Rule 501G, Fig 2. Thus the requirement for the 3rd target. In early 1959, when CTC was extended to include from Congress Park to West Hinsdale, Main 1 was made bi-directional between these two points, and the 3rd target was removed.
A similar 3rd target was installed on the Main 3 Westward signal at MP 17.50 at West Hinsdale, because Main 3 was an Eastward Main between West Hinsdale and Eola, therefore requiring the same signal aspect for a westward move on Main 3. When CTC was extended to Downers Grove in late 1959, this 3rd target was also no longer required.
Glen Haug