LOS ANGELES (CBS) —  Los Angeles transportation leaders plan to gather at Caltrans headquarters Monday morning to commemorate the 57th anniversary of what may be L.A.’s most iconic gift to the rest of the world: the SigAlert.

The world’s first automated traffic alert was transmitted by the Los Angeles Police Department’s AM radio station on Jan. 21, 1955.

Today, 57 years after radio engineer Lloyd Sigmon invented the SigAlert, the California Highway Patrol still uses that term to alert people to an unplanned lane closure of more than 30 minutes duration.

City council member Tom LaBonge said it is important for Angelenos to understand the history of SigAlerts, and of Sigmon, the “710-KMPC” executive and engineer who thought up the concept.

“There are so many people who went before us who did amazing things,” LaBonge told City News Service. “This man came up with a system that is now used by all the people to get around the challenges of the world’s largest freeway system.”

Sigmon was a vice president at Gene Autry’s KMPC, which in the pre-wired world of the 1950s revolutionized Southern California driving by launching a fleet of airplanes and helicopters to cover traffic during rush hours. But the “KMPC Air Force” could not fly day and night, and Sigmon wanted LAPD officers to phone KMPC when freeways or streets were clogged.

LAPD brass rejected that idea.

According to radio historian Harry Marnell, a SigAlert could be triggered by a watch sergeant at LAPD headquarters if he pressed a button to generate the tone on the LAPD radio system. At 11 commercial AM radio stations in L.A., Sigmon’s technology would prompt then-new reel-to-reel tape recorders to start up, and would flash lights or buzzers.

The news staff or announcers could then relay the breaking traffic news to the listeners. Chief William Parker approved the idea, but only if KMPC’s competitors could share the technology.

A train derailment triggered a SigAlert to call doctors to a smashed-up train from San Diego at the L.A. River near Washington Boulevard in 1956, where 30 people were killed and 122 were injured. Other SigAlerts that day summoned blood donors to hospitals.

SigAlerts were credited with saving the lives of hundreds when the Baldwin Hills Dam collapsed Dec. 14, 1963, and an unlikely flash flood washed north through houses and apartment buildings near La Brea Avenue at Rodeo Road. Five people were killed.

Sigmon’s theory is in use nationwide today in the form of the Emergency Alert System.

“It’s important we use this date in our history to remember the impact of this invention here,” LaBonge told CNS.

Sigmon moved to his native Oklahoma and died at the age of 90 in 2005.

The public is invited to the SigAlert celebration at 9 a.m. Monday outside the Caltrans building. 100 S. Main St.

“It will start at 9 —  unless there is a big SigAlert,” LaBonge promised.

(©2012 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services contributed to this report.)

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