I visited Zoo tower (viewed it through the fence). Probably the biggest tower I’ve ever seen! Last I heard it was still in service. Here in Ohio the last open tower is the Cleveland Drawbridge.
Zoo interlocking was always the largest interlocking in the world, it's called Zoo because it's near the Philadelphia Zoo.
I believe the largest interlocking now is somewhere in Japan.
Zoo interlocking was the in between for the Reading and the Pennsylvania Railroad separated by 30th Street Station. It was extremely difficult to be qualified on as an engineer but everyone had to be qualified at Zoo. I was only on the railroad for 5 years because I did not want to convert my Social Security to Railroad Retirement, as an engineer I was on the extra board meaning that I could not bid on a permanent job, I didn't have the experience but would fill in vacations, call outs, Protect Crews and yard crews.
To be on the extra board you had to be qualified on every line on both the Reading and Pennsylvania side, that's how I was able to be promoted into operations.
Interesting note that in the '80s I was probably one of the first people to be promoted who was not a mason, at that time it was not based so much on qualifications as it was your status as a mason.
Zoo interlocking is very much in use with some tracks out of service secondary to deteriorating tunnels and track. The tower is where the dispatchers operate from. It is Amtrak railroad attached to the Northeast Corridor, the Harrisburg line and the Marcus Hook line.
Interesting piece of my life but ended up going back to my other two careers I had before the railroad.
