Adler Alternate Flashing Relay

Automobile traffic increased significantly in the early 20th century, and so did collisions between cars and trains. Railroad companies installed warning signs and bells at crossings, but drivers ignored the signs, and motor noise drowned out the bells. Charles Adler, Jr., an inventor of traffic safety devices, tried signs that moved to attract the driver's attention. His 1921 STOP signal turned toward motorists when a train was approaching. In 1922, the Association of American Railroads chose a different signal—a pair of alternating flashing red lights—as the national standard. Adler devised a relay to create the alternating light pattern, and it was used by more than 40 railroads.
Currently on loan
date made
ID Number
accession number
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Credit Line
Amalie Adler Ascher
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Work and Industry: Transportation, Road
Road Transportation
Data Source
National Museum of American History, Kenneth E. Behring Center


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