A Sig Alert is defined by the California Highway Patrol as "any unplanned event that causes the closing of one lane of traffic for 30 minutes or more, as opposed to a planned event like road construction, which is planned separately." Sig Alerts are issued by the CHP and are posted on their Web site, broadcast on radio and television stations throughout California, and signalled to motorists via electronic billboards on the freeways. The term "Sig Alert" is as "real" as an English language word can be: in 1993, it was added to the New Shorter Oxford English Dictionary. (In practice, there is no standard spelling; the CHP Web site uses "SIG Alert," "SigAlert," and "Sigalert," all on the same page.)

SigAlerts originated in 1955 with the Los Angeles Police Department. By the early 1950s, the rapidly growing number of automobiles in Los Angeles had greatly increased the frequency and severity of traffic accidents and jams. Radio stations reported traffic conditions, but the LAPD refused to call radio stations with this information, so each station would call the LAPD, a process that tied up telephone lines and officers to repeat the same information again and again.

In 1955, Loyd C. "Sig" Sigmon began developing a solution. Sigmon was Executive Vice President of Golden West Broadcasters (a company owned by singing cowboy Gene Autry). Sigmon had worked for Golden West's station KMPC-AM 710 in 1941, but found himself in the United States Army Signal Corps during World War II, assigned to General Dwight D. Eisenhower's staff, in charge of non-combat radio communications in the European theater. Now, he proposed to apply his knowledge of complex radio networks to the situation in Los Angeles.

Sigmon developed a specialized radio receiver and tape recorder. When the receiver picked up a particular tone, it would switch on the tape deck and record the subsequent bulletin. The device cost about $600. The LAPD's chief, William H. Parker, was interested though skeptical, warning the inventor, "We're going to name this damn thing Sigalert." More practically, he refused to use it unless the receivers were made available to all LA radio stations -- it could not be a KMPC monopoly.

Initially, half a dozen stations installed Sigmon receivers that had "Sigalert" stamped on its side. When a message had been received and recorded from the LAPD, a red light, sometimes accompanied by a buzzer, would alert the radio stations' engineers. Depending on the nature of the problem, the engineer could air the police broadcast immediately, interrupting regular programming if necessary.

One of the first major "Sigmon traffic alerts" was broadcast on January 22 1956, causing a traffic jam. The alert described a train derailment near LA's Union Station and requested any available doctors and nurses to respond to the scene. Too many doctors, nurses, and sightseers drove there, making the situation worse. (The first SigAlert was on Labor Day weekend in 1955, and many stories on the SigAlert conflate these two events.)

At first, the LAPD issued about one alert a day, but soon other agencies were calling in messages they wanted broadcast, including rabid dog reports, gas leaks, and even a ship collision in Los Angeles Harbor. A druggist who had made a potentially fatal error in filling a customer's prescription took advantage of the system (who heard the SigAlert in time). It was also used to warn about the impending Baldwin Hills Dam collapse in 1963.

In 1969, when the CHP assumed responsibility for freeway traffic from the LAPD, they took control of the SigAlert system as well. It is now used throughout California and limited to traffic situations only. Messages are still broadcast, but most radio stations now read the information from the CHP's Web service rather than rebroadcasting the police dispatchers' voices.

References

• SigAlert!
• Snopes Urban Legends
• Current SigAlerts