What is SigAlert?

Article Details
  • Written By: Holly Collins
  • Edited By: Bronwyn Harris
  • Last Modified Date: 24 February 2020
  • Copyright Protected:
    Conjecture Corporation
  • Print this Article
Free Widgets for your Site/Blog
Apollo 17 astronaut Harrison Schmitt discovered he was allergic to the moon dust that ended up in the lunar module.  more...

March 31 ,  1889 :  The Eiffel Tower opened.  more...

SigAlert is a term coined in Southern California. It is partially defined by the California Highway Patrol (CHP) as “any unplanned event that causes the closing of one lane of traffic for 30 minutes or more.” The word SigAlert was added to the Oxford English Dictionary in 1993, but the CHP does not recognize a specific spelling of the term. SIG Alert, SigAlert, and Sigalert are all used on the official CHP website.

A SigAlert is issued by the CHP via radio, television, or on their website. Scrolling electronic messaging signs found on many California freeways also display these announcements. Originating in Los Angeles County in 1955, SigAlerts have become common throughout the state of California.

The high volume of automotive traffic in California, combined with an extensive freeway system, has resulted in a situation where even the smallest of roadway mishaps can have a major effect on a large number of drivers. This can result in severe back-ups and cause significant delays. The SigAlert system allows real time traffic information to be disseminated to a large audience quickly and efficiently.


Loyd C. Sigmon, known to friends as “Sig,” invented the SigAlert in 1955, in response to the problems the high traffic volumes were causing. Back then, media outlets would phone the Los Angeles Police Department (LAPD) seeking information about traffic accidents and delays. The Chief of Police did not want his officers tying up their time answering such inquiries instead of policing Los Angeles’ streets, so calls frequently went unanswered.

Sigmon had radio networking experience from his time in the U.S. Signal Corps during World War II, where he was in charge of non-combat radio communication. He used this expertise to invent a specialized radio receiver and tape recorder system, allowing LAPD officers to call and record traffic-related messages specifically to this system. The receivers were programmed to react to a particular tone that would engage the tape to record messages. LAPD officers could leave information on the tape from wherever they were in the field.

Local media outlets would be alerted by a buzzing sound or red light on their receivers indicating that a new message had been recorded. They could then quickly and efficiently relay that message to their audience. The system was a hit and quickly made available to a wide variety of media outlets.

The SigAlert procedure has evolved with technology and now operates via web alerts, email and other modern day communication methods. SigAlert messages are still displayed on electronic roadway signs and over radio and television airways. Although the SigAlert name is a tribute to its inventor Loyd Sigmon, a California joke attributes the acronym SIG to “stay in garage.”


You might also Like


Discuss this Article

Post your comments

Post Anonymously


forgot password?