The following was sent to me. I have not confirmed the information.

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Date: Wed, 5 May 2010 06:47:58 -0400
Subject: Interlocking Towers & Armstrong Levers


Subject: [Railway-Signaling] End of an era: no more mechanically-operated
switches in the USA

On Sunday, May 2, Union Pacific maintenance personnel removed from service
the single remaining mechanically-operated switch and its accompanying
facing point lock at Ridgely Tower in Springfield, Illinois. With this
retirement, there are no longer any interlocking plants in the USA which
operate switches connected via iron pipe to the tower's strong-arm levers –
referred to as "Armstrong" by some.

The principle of centralizing the operation of switches and signals first
originated in Britain in the 1850s, and the principle of interlocking them
to prevent unsafe sequences of operation followed soon thereafter. The only
form of power found practical in the beginning was provided by the human
body; as the towerman operated a lever, the motion was transferred to in
iron pipeline through bell cranks, slides, pulleys, etc., running up to
several hundred feet to the signal or switch operated by the lever. The
pipeline had to be compensated for thermal expansion and contraction as the
ambient temperature changed, and it had to be regularly lubricated and
adjusted. Derailments could put the pipeline out of service or knock the
pipes out of alignment, making them difficult to operate. Snow along the
pipeline would often thaw and then freeze, causing difficulty. Proper
maintenance worked wonders, but even in the best of condition, the leverman
needed a strong back and strong arms to do his job – hence the nicknames
given to these levers.

Over the years, I've had the opportunity to operate a number of mechanical
switches. The best operated with just a modest effort, but I can attest
that
the worst were backbreakers. Sometimes it wasn't the sheer force that
mattered, but the right "twist" on the lever as it moved through its
quadrant. After being slightly short of breath after lining a dozen
hard-to-throw switches a few hundred feet away from the tower, it was
rewarding to pull the last lever and watch out the window as the semaphore
blade moved skyward with the motion of my hands.

As various state legislatures passed laws in the late 1880s and 1890s
requiring a stop at crossings and junctions that weren't equipped with
interlockings, the number of interlocking plants proliferated. At the top
of
the list was Hammond, Indiana's State Line Tower, built in 1897 and having
224 levers – the largest mechanical interlocking in North America.

By the start of the 20th century, hydraulic, pneumatic, and electric power
was being harnessed to operate railroad switches and signals. As late as
1990, several dozen towers using brute mechanical force to throw switches
and clear signals remained in service. One by one they disappeared –
Chicago's 75th Street in 1997, State Line in 2000, East Chicago's Grasselli
in 2007. With the closing of CSX's towers in Hancock and Keyser, WV in
2008,
Springfield's Ridgely Tower became the unlikely holder of the title "Last
Mechanically Operated Interlocking in the USA."

But now there are none. There are a few remaining towers that still use the
old "strong-arm" levers; Dolton and Calumet are the last two in the Chicago
area, and there are but a couple more scattered around the country.
However,
the mechanical pipeline at these towers was severed long ago, and the old
levers at these locations do little more than open and close electrical
circuits that operate the switches and signals at trackside.

Ridgely Tower itself is on borrowed time. The removal of the last
mechanically-operated appliances there Sunday was necessitated by the work
underway there to rearrange the crossing and interchange tracks between UP
(ex-GM&O) and I&M (ex-CI&M), and to eliminate the tower. The tower
operators
have been served the formal notice required by their contract, stating that
their jobs will be abolished on or about June 7.

When Ridgely closes some time in June, an era will end for Springfield – a
city that had five active interlocking towers into the late Seventies. And
one more vestige of the Chicago & Alton's heritage will be gone.

But the era of mechanical interlocking plants has already ended this
weekend. That this technology originating around the time of the Civil War
persisted into the second decade of the 21st century is a testament to the
ingenuity of those who sought to ensure the safe operation of trains long
before electricity was harnessed and long before digital computers.

My hat is off in salute to those who designed, maintained, and operated
this
fascinating equipment that played a significant role in the history of
railroading.