Interlocking towers F
orm follows function in many railroad structures, as it often does elsewhere. Think of round- houses, sanding, water and coaling towers, icing platforms, turning facilities and interlock- ing towers. These last-named buildings were probably the most common of this lot but are now becoming ever more rare as train movement control becomes more centralized and computer assisted. Standing two or more stories high, often narrow in width and length, frequently with a square footprint and lots of windows on the upper floor, they were required where junctions, crossovers or switches fanned out to create multiple track routes, and at terminals and yards. From this high perch the towermen or signalmen had an overview of their territory and equipment and the trains within the “plant,” as the complex was called. Their intricate mechanical and/or electri- cal systems prevented the creation of conflicting routes, providing for safe and efficient movement of passenger and freight trains. Originating in England and reaching North America, these sys- tems became more sophisticated and less purely mechanical over time. The original arrangements employed combinations of wires, cables and pipes, rocker arms, pul- leys and bell cranks to throw switches, signals and derails. Many of the plants required a good deal of strength to move yards of steel linkages. Some mechanical advantage was provided by the tall levers in the towers, and the clicking of foot pedal or release on a lever would be followed by a reas- suring metallic “thunk” as the lever, passing through approximately a 30-degree vertical arc, went home. It wasn’t only strength, however, that moved the systems. Most interlockings had subtle idiosyncrasies that had to be learned when “posting the job” or from trial and error. Those working in northern climates quickly found that freezing weather, ice, snow and thermal expansion could make “lining the plant” very difficult. Most of them had an assigned maintainer for at least one shift, or trick. This employee usually resided in the first floor where he had a desk, locker, tools and lubricants to keep things functioning. This included snow shovels, “snow oil” and ice chipping tools for the winter. Also needed were rectangular metal containers with a large wick at one end and a kerosene filler hatch at the other. These sat between switch ties and directly under rails and points, burning night and day. Propane and electric switcher heaters are employed today. Late in the nineteenth century and early in the twentieth, electrical and pneumatic interlock- ings were installed. They reduced the need for sprawling mechanical rod systems and bell cranks but did not necessarily replace them completely. Some older mechanical plants retained the tall levers, but they then served as large electrical switches controlling electric motors to operate switches and signals. Others had complete, modern electrical controls that were handled from a small console not unlike that of many model railroads. Others were a combination of both old and modern systems. This was particularly true as centralized traffic control came into use after the 1920’s. It wasn’t until 2010 that the last all-mechanical tower, Ridgely Tower, built by the Chicago & Alton (now part of the UP system) where it crossed the Chicago & Illinois Midland in Spring- field, Illinois, closed, bringing the true “Armstrong” plant era to a close. Above the levers was a model board, a schematic of the tracks within the plant. Small lights indi- cated track occupancy and often switch and signal indications. An adjoining chart outlined the se- quence of operations to be performed to allow particular train movements. A desk had the OS sheet on which a record of all train movements was carefully maintained. Each arrival and departure was reported to the dispatcher who then inked them on his larger, comprehensive daily sheet. Tow- ers communicated with each other and also recorded weather conditions and other information the dispatcher or the particular job required. Train orders–operational directives issued by the dispatcher–were delivered at most towers. Special signals indicated when orders were to be delivered to both engineer and conductor. They were handed up by order forks or hoops or from fixed metal stands. Certain order forms required the train crew to stop to receive them. Company messages, in addition to movement directives, could also be passed on by towers. Officially, visitors were not permitted in the towers. However many towermen welcomed compa- ny who helped to pass the slow time between trains. It was an excellent place to observe the indus- try. Work shifts (known as 1st through 3rd tricks) were usually eight hours long changing at 7:00 a.m., 3:00 and 11:00 p.m. Depending on the location and traffic, however, not all towers were manned every day or for a full 24 hours.
ROBERT E. MOHOWSKI 40
AUGUST 2012
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