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The railway signaling industry encompasses
both the highway crossing signals (active warning devices) and wayside
signaling (the use of signals to control train movement).
Although the date of 1814 is given as the first
practical use of George Stephenson's invention, the steam locomotive,
railway signaling is even older. The first rail cars were pulled
by horses or mules and were used in mines and quarries. Records as
early as 1806 show that hand and arm signals were used to direct the
drivers of these early "trains". Hand signals, flags -
and at night, lanterns - were used to signal Baltimore & Ohio trains
in 1829. In some instances, a mounted flagman preceded the train
to warn of an approaching train - this custom continued in New York
City, on West St., as late as the nineteen twenties.
Signaling using fixed wayside signals probably first
began, in the United States, on the New Castle and Frenchtown R. R., in
1832. This 17-mile long railroad, connecting New Castle, Delaware
with Frenchtown, Maryland, used fixed signals, flags at first and later
ball signals, to pass information from one terminal to another.
In the early day of railroading, trains were operated
(more or less) by schedules. Thus train separation was a time
separation. As traffic increased, tracks were divided into blocks,
and train separation was by space interval. Thus block signaling
began. Various electrical and mechanical systems were tried.
Basically, they were designed to let one train pass into a block and to
inhibit the block entering signal from clearing to allow another train
into the block until the first train was reported to have left the
block. Later systems added a permissive feature, allowing trains
to follow each other into the same block.
Beginning in 1851, the electric telegraph was used to
determine the locations and progress of trains along the line and to
transmit train orders to expedite traffic.
These systems all required substantial manpower and had
no protection against a part of a train being accidentally left in a
block between signal stations.
August 20, 1872, marked one of the most important events
in railway signaling, the invention of closed track circuit by Dr.
William Robinson. First installed at Kinzua, Pa. on the
Philadelphia and Erie RR., the closed track circuit soon proved its
worth, and other installations followed rapidly. All modern track
circuits are based on Dr. Robinson's original concept, even though their
capabilities have been greatly amplified by modern track relays, coding,
and more recently, electronic techniques such as the high-frequency
jointless track circuits.
The track circuit is used to detect the presence of a
train or a broken rail within a block of track. When an electric current
traveling through the rails in a block of track is shorted by the
presence of a train or interrupted by a break in the rail, a red signal
indicates danger to approaching trains. When the track is clear, the
closed circuit activates a green signal to indicate that approaching
trains can enter the block. The same circuit principle is also used to
activate highway crossings.
The railway signaling industry encompasses
both the highway crossing signals (active warning devices) and wayside
signaling (the use of signals to control train movement).
Although the date of 1814 is given as the first
practical use of George Stephenson's invention, the steam locomotive,
railway signaling is even older. The first rail cars were pulled
by horses or mules and were used in mines and quarries. Records as
early as 1806 show that hand and arm signals were used to direct the
drivers of these early "trains". Hand signals, flags -
and at night, lanterns - were used to signal Baltimore & Ohio trains
in 1829. In some instances, a mounted flagman preceded the train
to warn of an approaching train - this custom continued in New York
City, on West St., as late as the nineteen twenties.
Signaling using fixed wayside signals probably first
began, in the United States, on the New Castle and Frenchtown R. R., in
1832. This 17-mile long railroad, connecting New Castle, Delaware
with Frenchtown, Maryland, used fixed signals, flags at first and later
ball signals, to pass information from one terminal to another.
In the early day of railroading, trains were operated
(more or less) by schedules. Thus train separation was a time
separation. As traffic increased, tracks were divided into blocks,
and train separation was by space interval. Thus block signaling
began. Various electrical and mechanical systems were tried.
Basically, they were designed to let one train pass into a block and to
inhibit the block entering signal from clearing to allow another train
into the block until the first train was reported to have left the
block. Later systems added a permissive feature, allowing trains
to follow each other into the same block.
Beginning in 1851, the electric telegraph was used to
determine the locations and progress of trains along the line and to
transmit train orders to expedite traffic.
These systems all required substantial manpower and had
no protection against a part of a train being accidentally left in a
block between signal stations.
August 20, 1872, marked one of the most important events
in railway signaling, the invention of closed track circuit by Dr.
William Robinson. First installed at Kinzua, Pa. on the
Philadelphia and Erie RR., the closed track circuit soon proved its
worth, and other installations followed rapidly. All modern track
circuits are based on Dr. Robinson's original concept, even though their
capabilities have been greatly amplified by modern track relays, coding,
and more recently, electronic techniques such as the high-frequency
jointless track circuits.
The track circuit is used to detect the presence of a
train or a broken rail within a block of track. When an electric current
traveling through the rails in a block of track is shorted by the
presence of a train or interrupted by a break in the rail, a red signal
indicates danger to approaching trains. When the track is clear, the
closed circuit activates a green signal to indicate that approaching
trains can enter the block. The same circuit principle is also used to
activate highway crossings. |
