SigAlert : Loyd Sigmon’s Invention Still Travels the Airwaves After 36 Years


A SigAlert was issued Thursday morning from the front seat of a white Cadillac stuck in a traffic jam on the southbound San Diego Freeway.

Loyd Sigmon shook his head at the crush of cars inching along with him out of the San Fernando Valley and turned to his passenger in the back seat.

“I’m not sure I’m going to forgive you for getting me into this ,” Sigmon warned. “This traffic is miserable. I’ve just about had it.”

Sigmon, 81, had every right to issue the personal advisory. He invented the SigAlert. His passenger had coaxed him into the miserable 8 a.m. rush-hour traffic to check on the effectiveness of his world-famous traffic warning system after 36 years.

As it turned out, there were no wrecks or overturned big rigs or attractive brunettes changing tires in the center divider to cause the jam. There were just too many cars.


So there was no reason for a real SigAlert to be issued for the Sepulveda Pass as Sigmon crawled up the hill in his car with the SIGALRT personalized license plate.

Things were different in 1955 when Sigmon, then an executive at radio station KMPC-AM 710, devised the SigAlert system.

Freeway congestion was rare in those days unless there was a crash. That made freeway wrecks, which were investigated by the Los Angeles Police Department, big news.

Sigmon decided he could boost his station’s ratings if he could get the police to call him whenever a major wreck occurred so KMPC could broadcast the news.

When police balked at spending the time on the telephone, Sigmon set out to devise a machine that could tap into the department’s regular radio dispatching center.

He built a receiver-tape recorder setup that would automatically switch on when activated by an inaudible “subcarrier” radio tone transmitted by a police dispatcher. After the dispatcher’s advisory was recorded, a red light would alert the radio station engineer that it was ready to be played back and put on the air.

Police Chief William Parker approved of the concept--after he made Sigmon make his $600 invention available to every radio station in town that wanted it.

The very first SigAlert advisory was broadcast by six radio stations on Labor Day, 1955. It ended up causing a traffic jam, Sigmon said.

“It was a train accident out of Union Station. Some rail cars flipped over and they put out a request for doctors and nurses,” he said. “So many people responded that it caused a tie-up at the scene.”

During its first three months, 86 SigAlerts were issued by Los Angeles police, who soon were receiving messages from other nearby police agencies to transmit over Sigmon’s system.

But only 36 were traffic advisories, according to city records.

Among the early bulletins were five warnings of rabid dogs, two for pharmacists’ “mis-filled prescriptions,” several about air raid siren tests and even one about a ship collision in Los Angeles Harbor.

But the system was a wild success. Magazines and newspapers across the country reported on it. The voices of police dispatchers who delivered the advisories became almost as famous as those of some radio station deejays.

A pleased Chief Parker dubbed the network the “SigAlert” system in honor of Sigmon, whose nickname is “Sig.” But in early 1956, when Mayor Norris Poulson took to the airwaves on KFI-AM 640 to formally announce the system, he sparked confusion that still exists.

“Just as the name implies, the SigAlert system has to do with sending out a signal,” the mayor mistakenly announced.

These days, “the single most-asked question I still get is, ‘What is a SigAlert?’ ” Bill Keene, the dean of Los Angeles’ traffic reporters, said.

Keene looked up from the shelf of CHP radios and Caltrans computer screens at his tiny traffic monitoring studio at radio station KNX AM-1070 when Sigmon walked in. The California Highway Patrol now issues freeway advisories. But tie-ups that are expected to last 30 minutes or more are still called SigAlerts.

So many of them pour in each day--there were about 15 issued Thursday morning, Keene said--that radio stations now summarize SigAlerts instead of broadcasting the CHP dispatchers’ voices, he said.

“Loyd, your name’s really being used in vain today,” Keene said, grinning. “There are SigAlerts all over the place. I’m handling SigAlerts out my ears, thanks to you.”

Keene and Sigmon agreed that none of Thursday’s tie-ups matched their favorite SigAlert--a seafood truck wreck on the Harbor Freeway a few years ago. Highway patrolmen struggled to clean up the mess and reopen the traffic lanes.

“We had fish and CHiPs all over the place,” Keene said.