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In the early 1800's, the earliest rail signaling systems employed signalmen
standing along the track at intervals within sight of each other, signaling with flags or hands to communicate train location and movement. The 1800's saw a succession of advances, from fixed signal posts to telegraphed train orders and signaling information. Until the 1870's, however, all signaling was controlled manually and therefore subject to human error.
The patented invention of the electric closed track circuit by Dr. William Robinson in 1872 gave the railroad industry its first means of automatic vital signaling.
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.
In 1878, Dr. William Robinson founded the Union Electric Signal Co. to hold his patents, to produce track circuits, and to install them. This technology continues to be a foundation of rail signaling and communications today.
As the rail system grew in the 1800's, tracks began to cross, giving rise to junctions, at which coordination between switches and signals was needed for safe and efficient operation. The first step in this coordination was concentrating the control of switches and signals in one location, first implemented in England. In the late 1850's, the separate switch and signal controls were interlocked so that their movements would succeed each other in a predetermined order. This technology was imported to the United States in the early 1870's, and in the mid-1870's, the first U.S. company was formed to manufacture interlockings.
It was upon these two innovations - the closed track circuit and the interlocking - that Union Switch & Signal was founded. George Westinghouse formed US&S by consolidating the Union Electric Signal Company - holder of closed track circuit patents - and the Interlocking Switch & Signal Company - holder of interlocking patent rights.
From this dynamic start, US&S has pioneered countless incremental advancements and milestones of lasting significance to the rail signaling industry.
- 1903: first AC track circuit & vane relay
- 1923: first inductive train control (continuous cab signaling system)
- 1923: first industrial application of vacuum tubes
- 1924: first remote controlled gravity hump yard
- 1926: invention of copper oxide rectifier
- 1934: first coded track circuit
- 1942: first coded carrier centralized traffic control (CTC) system
- 1966: first computer aided dispatching system
- 1970: first digital classification yard control system
- 1985: first microprocessor-based vital interlocking
- 1986: first video-projection railroad territory display
- 1987: first consolidation of control of all rail territory in one location
- 1995: first driverless-capable light rail transit (LRT) system in North America
- 1998: first fully consolidated transit operations control center
- 2000: first advanced speed enforcement system
- 2002: first completely driverless metro system
Over the past century, US&S has developed solutions for a variety of conditions faced by train operators.
- The need for failsafe (or vital) signaling.
- The need to control train speeds automatically.
- The need to manage and monitor rail traffic patterns.
- The need for efficient train assembly in yards.
- The need for signaling and control in high-speed environments.
We have improved and refined our solutions by applying ever-more-sophisticated technology: electricity in the 1800's, electronics in the 1920's, coded track circuits in the 1930's, transistors and computers in the 1960's, microprocessors in the 1980's, and radio control in the 1990's.
We continue to live up to our legendary record of pioneering advancements in signaling and control technologies for railroad and transit systems in North America and worldwide. We're applying automation and information technologies to a future of "smart" trains run by our computerized control systems, providing automated and fully integrated operations control.
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