In this segment from The Henry Ford's Innovation Nation, Mo Rocca meets with curator of transportation Matt Anderson to learn more about railroad crossing signals.
Before automated signals became common, the busiest railroad crossings were protected by railroad employees. A person was stationed at the crossing and, when necessary, manually activated a signal or a gate, or perhaps simply waved a flag, a sign or a lantern, to warn approaching road traffic.
Wigwag railroad crossing signals -- named for the way they swung back and forth when activated -- first appeared about 1914. Their waving action simulated the motion of a lantern being swung back and forth -- long a signal for "stop" on American railroads. Typically, wigwags were driven by a pair of electromagnets that alternately pulled and released the pendulum.
Automatic railroad crossing signals are controlled through an electrical relay in the railroad track. A low-voltage electric current is sent between the two rails via a series of relays. When a train approaches, the current runs through the train's metal wheels and axles instead of the relays. This "short circuit" activates the crossing signal.
Automated gates first appeared in the 1930s. Four-quadrant gates completely block off the road, while more common two-quadrant gates block each lane only in the direction of travel.
Check out our curated expert set to learn more about railroad crossing signals: www.thehenryfo...
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27 авг 2024
