Images of 75th Street Tower, Chicago, Illinois

CSX's Seventy Fifth Street Tower in Chicago, Illinois was one of my all-time favorite spots from the time I discovered it in the early Nineties to the day it closed in November, 1997. The interlocking was without a doubt the biggest collection of ancient signal hardware I have ever seen, and I consider myself fortunate to have been able to witness and document this fascinating part of our signal heritage before it disappeared.

Here are just a few of the photographs that I took at the tower over the years.

Copyright © 1994-1997 by Jon R. Roma.
All rights reserved.

North view of tower

This image was taken from alongside the CSX (B&OCT) main line and looks in a southeasterly direction. Taken in 1997, the resignaling work can be seen in the form of the new aluminum ground mast signals in the foreground and the cantilever signals in the background. Not yet activated, the signals are turned away from view by approaching trains. The westbound color position light home can be seen beyond the cantilever signals.

To the left of the tower door can be seen the cable line that led to the north end of the plant. The pipe line can barely be made out along the ground to the east (left) of the tracks.

Dwarf semaphore

This tasty little semaphore governed wrong-current moves on the Belt Railway of Chicago moving geographically east from Clearing Yard toward Belt Jct. The pipe operating this upper-quadrant semaphore can be seen in the foreground and to the right.

High semaphore

This two-arm high semaphore governed moves on the BRC main line moving geographically east from Clearing Yard toward Belt Jct. The pipe operating this signal runs parallel to the signal mast and connects to the semaphore unit near the fulcrum.

Since the mechanical BRC signals at 75th Street did not convey track occupancy information, only the lower blades were operative, denoting a Restricting indication.

Interior view of tower

This photograph was taken from behind the locking bed at the south end of the tower's operating room. The view looks northwesterly on a sunny afternoon toward the operator's desk. In the foreground is the rightmost (high-numbered) end of the 132-lever mechanical interlocking machine. Note the boxes of bottled water stacked on top of the locking bed's canvas cover; the tower had no running water.

Lever bed

This time exposure of the lever frame and locking bed were taken on a fall evening a couple months before 75th Street Tower closed. The view looks northeasterly toward the low-numbered end of the lever frame. Through the tower's north window can be seen the same pole line shown in the earlier outside view. Note the red and yellow signal flags mounted on the tower's freshly-painted back wall.

Manipulation chart

This view shows 75th Street Tower's manipulation chart. Listed are each possible route through the plant. On the model board (shown below), each entry and exit point from the plant is marked with a letter. The manipulation chart indicates for each route (say for C to L) which levers had to be reversed to complete the line-up. Some 60 distinct routes were possible within the 75th Street plant, and some required operating up to 11 levers.

As most of these levers were mechanically connected by pipe line to appliances at trackside, serving as operator/leverman at 75th Street required a strong back. While most of the levers operated smoothly due to regular lubrication, some were rather stubborn due to the distances involved -- especially when snow and ice covered the pipe lines.

Model board

The model board was mounted in the southeast corner of the tower near the operator's desk. The orientation of the track diagram is the same as the operator's view facing the interlocking machine, so east is to the top of the model board. A small rectangle representing the tower can be seen near the center of the diagram.

The vertical lines represent (from left to right) the double-track Belt Railway of Chicago and Norfolk Southern (former Wabash) main lines that passed through the plant in an east/west direction. The horizontal pair of tracks is the CSX (former B&OCT) main line. Lamps on the board show occupied track circuits, one of the few concessions to modernity at 75th Street. From this view, it appears that a BRC train is passing through the plant, and a Wabash and three CSX trains are stopped outside the home signals. Black paint covers the PRR "Panhandle" line (above the CSX main) which was abandoned in the early Eighties.

View of pipe line from tower window

This view from the tower's west window shows the CSX (former B&OCT) tracks, the pipe lines passing underneath the tracks, and the cranks which changed the pipe motion's direction by 90 degrees. The pipe lines shown operated the appliances on the Belt Railway of Chicago and Norfolk Southern west of the crossing.

The light winter snow on the ground is probably not sufficient to cause difficulty operating the pipes.

Close-up of pipe line

This is a closer view of the pipe line and two cranks leading to trackside signal appliances. Most likely, one of these lever controlled a derail and the other lever controlled the facing point lock which locked the derail into place.

In the right foreground can be seen a close view of one of the pipe carriers used to support the mechanical pipe line and keep it properly aligned. The smooth operation of the pulleys and cranks was assisted by regular lubrication and one can see evidence that the signal maintainer has been keeping the appliances oiled.

Overhead view of lever frame

In this photograph taken from atop a ladder, one can see the operating levers and lever quadrants, as well as the locking bed and the mechanisms which transferred motion from the lever to the latitudinal locking bars.

Levers 88, 89, and 90 were spare spaces provided in the frame and lack some of the hardware present for the active levers. It was customary to provide spare spaces at strategic locations in the frame to allow for subsequent addition of levers required for new track connections and so forth. In some cases, spare levers with all the accompanying hardware were provided. To my knowledge, these spare spaces were never used during 75th Street Tower's 79-year lifetime.

Name plate on machine support

This view shows the machine support just below the tower's second floor and looks toward the front of the machine. Cast into the support are the words

THE FEDERAL RAILWAY SIGNAL CO. TROY, N. Y.

While Union Switch & Signal obtained U. S. production rights to the improved Saxby & Farmer machine, most of the competing signal manufacturers (such as Federal) began to offer the popular S. & F. frame once the patents had expired.

Lever connections

This photo is taken below the lever bed and facing toward the operator. Shown are the vertical pipe connections to the lever tails. These pipes are also connected at ground level to vertical cranks or rotary cranks, depending on the direction to which the pipe will leave the tower toward trackside.

Counterweight

Some of the signal levers at 75th Street Tower were equipped with counterweights, to compensate for the relatively low resistance associated with these levers compared with switch point levers. This view is inclined upward toward the locking floor, facing in the same general direction as the operator would face the lever frame.

One of the long-time railroaders at 75th Street recalls that due to its proximity to the tower, the eastbound home signal semaphore on the PRR was particularly easy to operate. When restoring a signal lever to normal, all one had to do was squeeze the lever latch; the counterweight would throw the lever back normal without any further effort on the operator's part!

Vertical cranks

The vertical pipe line connected to these cranks is connected to the lever tails just above the ceiling of the tower's first floor. The cranks transfer vertical motion to horizontal motion to operate switch points, facing point locks, and signals at trackside.

Vertical cranks

Here's another view of vertical cranks, showing how the vertical motion transmitted by the levers is transferred to a horizontal motion in a direction perpendicular to the locking bed.

Rotary cranks

This photo shows rotary cranks and is taken standing facing the interlocking machine, albeit on the floor below the machine. The vertical motion from the lever tail above is transferred to a horizontal motion to trackside via these rotary cranks.

Rotary cranks

This is a rear view of the rotary cranks. Motion is transmitted from the lever tail above to the cranks, which pivots the bars in foreground. Bolted to each bar is a pipe which is connected to a set of switch points, facing point lock, or signal. Both vertical cranks and rotary cranks transfer vertical motion from the lever tail to a horizontal motion. The vertical cranks shown in earlier images are used to transfer motion in a direction perpendicular to the lever frame, while rotary cranks are used to transfer motion in a direction parallel to the frame.

Seventy Fifth Street Tower had pipes exiting all four sides of the tower.

Bolt lock

A bolt lock is a cross-check on proper switch alignment before a signal can be cleared. Of course, any signal lever is released in the locking bed only by the route's switch levers and facing point lock levers being in the proper position. This check is insufficient in the event the pipe line became disarranged between the interlocking machine and the switch points; this defect could allow the signal lever to be released improperly. The bolt lock physically prevents the pipe line operating the signal from being moved if the switch points do not lie in the proper position.

Compensator

Compensators are placed in the pipe line at strategic intervals to compensate for the expansion and contraction of long runs of pipe line as temperatures change. A compensator consists of an obtuse and acute crank joined together. Note that a compensator reverses a "pull" on the pipe at one end to a "push" on the other end.

Deflecting bars

Deflecting bars changes the direction of pipe motion by means of arc-shaped bars attached to pipes at each end. Pipeline motion causes the deflecting bars to slide in their slot, transmitting the motion to the pipe at the other end of the bar. In this case, the deflecting bars are used to change the pipe line direction 90 degrees.

Facing point lock

A facing point lock's purpose is to lock switch points in their proper position prior to clearing a route over those points. The reversal of the facing point lock (FPL) lever drives the locking bar (perpendicular) into notches attached to the switch point. Clearing a route requires reversal of all FPLs protecting that route. If the switch points are not in position, the FPL lever will not reverse, preventing a signal from being cleared if the switch is not in proper position.

Jon Roma <roma@uiuc.edu>
April 17, 2000