Gresham Tower
Chicago, Illinois
Gresham Tower was built in 1952 for the Rock Island Railroad; it housed a "Sequence Switch Interlocking" machine. Only three of these interlocking machines were installed in service, two of them in Britain and this one in Chicago. This interlocking machine uses components that are commonly used for telephone switching. The interlocking machine was made by Standard Telephones and Cable Limited of London, England. The model board also was unique in the fact that you would have a entrance signal and an exit signal. The entrance signal would have several numbers for the possible exit. You would rotate the entrance signal to the corresponding exit signal and press the button and the machine would do the rest. Metra closed the tower in 2010.
This is Gresham's model board, it has entrance signal levers, route levers, and manual switch control knobs. There are lighted switch indicators in the track layout to indicate the position of the switch.
This is one of the many cabinets that housed the "sequence switches."
This is the same cabinet as above just the doors opened. You can see that the sequence switches are driven by gears to the left of the cabinet. One row of sequence switches controls approximately one signal.
