What is a "Sig Alert"?

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.

http://en.wikipedia.org/wiki/Sig_Alert

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.)One of the first major "Sigmon traffic alerts" was broadcast on January 22, 1956, causing a traffic jam. The alert described the derailment of the Santa Fe's San Diegan passenger train 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.

"Sig-Alerts" are unique to Southern California. They came about in the 1940s when the L.A.P.D. got in the habit of alerting a local radio reporter, Loyd Sigmon, of bad car wrecks on city streets. These notifications became known as "Sig-Alerts." Later Mr. Sigmon developed an electronic device that authorities could use to alert the media of disasters. Caltrans latched on to the term "Sig-Alert" and it has come to be known as any traffic incident that will tie up two or more lanes of a freeway for two or more hours.