The Amazing History of the SigAlert System

A SigAlert is issued by the California Highway Patrol when two or more lanes of traffic will be closed for an unexpected reason for 30 minutes or more. It is an attempt by the California Highway Patrol to warn motorists to avoid a particular area. The term has become so familiar that it was added to the Oxford English Dictionary.

SigAlerts can be issued for accidents involving cars, motorcycles, pedestrians, or any other roadway hazard that will unexpectedly keep roadways closed in excess of 30 minutes.

The idea for SigAlert came from Loyd C. Sigmon who was the station manager at AM radio station KMPC. He approached Los Angeles Police Chief William Parker about installing the system. Sigmon had served as a radio engineer with the Army Signal Corps in Europe during World War II. The original system used a shortwave radio set to the Los Angeles Police Department’s frequency to transmit to a tape recorder. Sigmon could then push a button to turn on a red light in the studio. A special tone would then sound followed by the tape-recorded announcement from the police.

While no one recorded the first use of SigAlert for prosperity, one of the first uses was when a train derailed on January 2, 1956, as it was leaving Union Station in Los Angeles. The wreck killed 29 people and injured more than 120 people. The system was used to issue a plea for emergency responders to come to the scene to help. So many people heard the announcement and responded that it caused a traffic jam.

In the early days, the SigAlert system was used for a variety of purposes. In addition to just traffic alerts, the system warned citizens of gas leaks, rabid dogs and dam problems. The system was even used by a druggist to find a customer who he had fouled up their medicine. When two ships collided in the Los Angeles Harbor, Los Angeles Police Chief Parker stopped using the system for anything but traffic alerts. Over time, some very interesting traffic SigAlerts have been issued like the time that 10 tons of pie overturned making a mess on the road.

When the California Highway Patrol took over monitoring the highways in 1966, they started using the SigAlert system, and it soon expanded statewide. The system soon went statewide. Any officer can sound the alert if he feels that traffic will be tied up for more than 30 minutes. There are no special signals at the scene of an accident or traffic congestion that tells motorists that a SigAlert has been issued.

Loyd Sigmon passed away in 2004 in Oklahoma. Before his death, he was honored by the National Council of Safety, the Los Angeles City Council and the California Highway Patrol for his invention. He always found it funny, however, that he ran the radio station for decades, but was remembered for this single invention that he never tried to patent and received no money for inventing.