Union Switch & Signal

Union Switch & Signal
Company type	Subsidiary (historical)
Industry	Railway signaling, communication technologies
Predecessor	Union Electric Signal Company, Interlocking Switch & Signal Company
Founded	1881
Founder	George Westinghouse
Fate	Acquired by Ansaldo STS in 1988; renamed Ansaldo STS USA in 2009; rebranded Hitachi Rail STS in 2019
Headquarters	Pittsburgh, Pennsylvania, United States
Area served	Americas, Asia
Key people	William Robinson (inventor of track circuit)
Products	Railway signaling devices, communication technologies, automatic train stop systems, level crossing signals, wayside signaling equipment, central control signaling equipment
Number of employees	900 (2005)
Parent	Ansaldo STS (1988–2009), Hitachi Rail STS (post-2019)

Union Switch & Signal (US&S) was a U.S.-based enterprise located in Pittsburgh, Pennsylvania, specializing in the manufacture and provision of railway signaling devices, communication technologies, and related services. Established in 1881 by George Westinghouse, US&S emerged from the merger of the Union Electric Signal Company—founded by William Robinson, who invented the track circuit—and the Interlocking Switch & Signal Company, innovators in interlocking systems. In 1925, US&S broadened its offerings by acquiring the Hall Signal Company, securing key patents for searchlight signal technology and enhancing its competitive stance.

From 1988 until 2009, the company functioned as a subsidiary under Ansaldo STS (which later became Hitachi Rail STS), before adopting the name "Ansaldo STS USA" to better align with its international operations throughout the Americas and Asia. Around 2005, US&S employed roughly 900 staff members and maintained a prominent role in the electronics sector, concentrating on cutting-edge railway signaling solutions that fueled its market strength and consistent growth.

Corporate management

US&S remained an independent entity until 1917, at which point it was incorporated as a subsidiary of the Westinghouse Air Brake Company (WABCO). In 1968, WABCO was acquired by American Standard, which reorganized US&S as a separate division within its structure.

In 1988, Ansaldo STS, a worldwide provider of signaling, control, and automation technologies, purchased US&S from American Standard. By November 1993, US&S had gone public with stock listed on Nasdaq. In December 1996, US&S merged with other signaling assets owned by Ansaldo and became a fully owned subsidiary; it was renamed Ansaldo STS – USA in January 2009. Following Hitachi’s acquisition of Ansaldo in 2019, the company was rebranded as Hitachi Rail STS.

Historically, US&S operated manufacturing facilities in Swissvale, Pennsylvania, near Pittsburgh; this plant ceased operations in 1985 and was demolished the following year. Production activities were subsequently relocated to Batesburg-Leesville, South Carolina, while research functions continued to be based in Pittsburgh.

Railway signaling

US&S introduced the first power interlocking system in the United States in 1882 at East St. Louis, Illinois. Initially employing pneumatic technology, it later evolved into electro-pneumatic systems that were widely adopted across American railroads.

In 1901, US&S created the first electro-pneumatic automatic train stop system for the Boston Elevated Railway; this technology was subsequently implemented by the New York City Subway and other transit networks. The company also launched an electrically operated highway crossing gate in 1908.

By 1923, US&S had developed the inaugural inductive train control system and advanced coded track circuits enabling bi-directional cab signaling by 1934.

In 1970, US&S delivered the first digital rail yard control system to the Atchison, Topeka & Santa Fe Railway in Kansas City, Kansas—representing a major milestone in railway automation and signaling innovation.

The "Teardrop" Mechanical Bell

On February 20, 1917, US&S secured a patent for the Model 15A Highway crossing bell. This bell, commonly referred to as the "Teardrop" due to its unique contour, gained international recognition throughout the 1920s, appearing in railroad signal promotions in countries such as Chile and Italy. Several variations existed, differing in coil dimensions and patent inscriptions; the most uncommon variant displayed only the inscription "UNION, patent pending." Collectors prize this bell for its distinctive slow and deep tone. Although manufacturing ended by the 1960s, WABCO continued providing spare parts into the 1970s.

Production During Wartime

In the First World War, Union Switch & Signal produced approximately 10,000 Le Rhône 9C rotary engines under license at their Swissvale facility, primarily for fighter aircraft. During the Second World War, US&S was one of five manufacturers contracted to produce M1911A1 pistols, completing around 55,000 units before contract cancellations in 1943 curtailed further production. These pistols are recognized for their exceptional craftsmanship and are sought after by collectors due to their limited quantity. Additionally, US&S supplied components for M1 Carbines under subcontract arrangements, with only Singer Manufacturing producing fewer pistols.

Level Crossing Signal

Level crossing signals:
- Model 95 gate mechanism
- Flashing lights available in 8" and 12" sizes
- Bells, masts, gate arms, and counterweights
Cab signaling devices
Systems for automatic train control
Automatic train protection solutions
Devices for automatic train stopping

Wayside Signaling Equipment

DC coded track circuit systems
Electronic communication technologies
Electronic interlocking systems
Relay devices
Railway signal apparatus
Switch machine units
Various Track circuit configurations

Central Control Signaling Equipment

Computerized manual control platforms
Computer-driven traffic management systems
Control solutions for Dark territory
Electro-mechanical machines for centralized traffic control

Note

US&S uniquely manufactured electronic bells with a 180-degree design.