Ah, towers! When I was a student in Chicago in the early 1970s, I befriended an ICRR towerman (Kensington day operator), and he and I visited essentially all the remaining towers in the Chicago region over the next several years. I wish I had taken more pictures! Even then, it was apparent that these towers were anachronisms, but some had stood for more than a century, so who could have predicted they would be abandoned so quickly?
Towers came about because of the need to control complex railroad junctions and crossings. Originally this was done with "switchtenders", people on the ground who hand-threw switches and signaled trains (with lanterns or flags) to proceed on the lined routes. As trains got faster and traffic volume increased, a way was needed to line routes and signal trains more quickly. The result was manual or "armstrong" interlockings, controlled by cranks and rods, allowing an operator to manipulate switches and signals from a central location (inside a station, in a one-story cabin, or -- more commonly -- on the second story of a "tower"). The first floor of the tower held an "interlocking" bed, a metal frame that physically prevented the tower operator upstairs from lining up conflicting routes.
For obvious reasons, these towers had to be close to the locations they controlled, since the instructions were transmitted by rods and cranks. The largest "armstrong" tower I ever saw was State Line Tower in Hammond, IN, which controlled Erie, Monon, South Shore, and Nickel Plate routes and had a couple of hundred man-sized levers.
Electric interlockings could do the same job as manual ones, and do it more efficiently, and they quickly became the railroads' choice in the early years of the 20th Century. They came in two basic flavors: "straight electric", in which switches and signals were controlled by electric motors, which in turn were controlled from a collection of levers and relays in the tower; and "pneumatic" interlockings, which were electric but which used compressed air to throw switches (and to operate signals, when semaphores were still in use). The PRR was very fond of pneumatic interlockings.
But once electricity was used, it was no longer necessary for the operator to be adjacent to the devices he was controlling. You could put him anywhere. In 1927, the Toledo and Ohio Central Railroad converted three towers at Leipsic Junction to remote operation, called "Centralized Traffic Control". When each tower had a separate operator, trains could get "gridlocked" (the towers controlled three junctions at the vertices of a triangle, less than a mile apart). With one operator in charge, the conflicts wouldn't occur. This was the first installation of CTC in the country, and all it did was replace the large interlocking machines with a miniature "model board". All the existing relay logic remained in the field. it was just controlled from a central location.
We haven't really progressed much farther in the subsequent 80 years. The fancy dispatch centers and "TCP/IP" code lines (or radio) are controlling the same old electromechanical relays and circuits the towers formerly did. Yes, a lot of jobs have been elinminated, but all that relay logic is still in the field, and has to be maintained.
It's time to replace the existing (obsolete) signal system. Much as I miss the towers, I think it's time for railroads to enter the 21st Century.
Randy Resor, aka "NellieBly" passed away on November 1, 2013. We honor his memory and his devotion to railroading at railroad.net.