How SigAlert Got Its Name (2024)


SigAlerts can be a harbinger of stress when you’re driving or using public transportation. They warn you of traffic jams. But did you know the alert system actually started as a way to share civil defense updates? We look into how SigAlerts began, and the man behind them.

What is a SigAlert? It’s any unplanned event that causes the closing of at least one lane of traffic for 30 minutes or more.

How did it start? It was created in the early ‘50s by Loyd Sigmon, a radio executive at L.A’s KMPC station. During the Cold War, civil defense officials were looking into how to make an alert system, a project that Sigmon developed.

So how did it get into traffic? It started out as a civil defense mass communication tool, but Sigmon also found a daily use for it: traffic alerts. He figured out how to make a special receiver that the LAPD could use to share a wide range of traffic updates.

There’s a term you’ve probably come across more than once while traveling around Southern California: SigAlert.

It’s one of the best ways to keep on top of traffic delays in near real-time, but they’re also a harbinger of stress. If a SigAlert is issued on your route, good luck getting to your destination on time. There could be a car stalled on the freeway, a car crash or any number of other problems shutting down lanes.

But do you know why they're called SigAlerts? They actually started out as a radio tool.

How did SigAlerts begin?

Before SigAlerts lived online in an interactive map, and were issued by the California Highway Patrol, they came from a specialized radio receiver that broadcast recorded messages.

In the early ‘50s, civil defense officials had been looking into how to make an alert system in case of an attack from the U.S.S.R., which became the brainchild of Loyd Sigmon, executive vice president at L.A.’s KMPC radio station.

What defines a SigAlert?

  • It’s any unplanned event that causes the closing of at least one lane of traffic for 30 minutes or more, according to its website.

The system was first officially tested in November 1954. In City Hall, officials pressed a red button that took KMPC off air and instead broadcast civil defense information to listeners. Think of it like a Cold War version of the emergency alert system — the idea was to get urgent updates out fast, like potential attacks or major flooding.

A number of Southern California broadcasters signed on to install the necessary equipment, including KNX. Devices were also installed at the offices of civil defense personnel to speed up the process.

Where to find SigAlerts

  • Yes, you can look up SigAlerts and other real-time traffic information yourself by visiting

Sigmon also thought of a more daily use for the system. He approached the L.A. Police Department with an idea: set up a process for police departments to call the station when major traffic jams occur. But that wasn't really feasible for officers to do every time.

It’s unclear how many times Sigmon customized devices to use the SigAlert system in different ways, but according to SigAlert researcher Harry Marnell, for the LAPD, he used a $600 shortwave receiver and tape-recording device that booted up with a special tone. The LAPD would receive details from other agencies and then press a button to record and send that special tone with the information to radio stations (like a high-stakes telephone game).

The system, which was put into widespread use in Greater L.A. on Labor Day 1955, was intended to tell the public about a range of concerns: major freeway tie-ups, smog alerts, fire, explosions, dense fog and “atomic” attacks.

Today, it’s just about major traffic delays. Relaying of emergency information lies with things like the emergency alert system. But Sigmon has gone down in history as pioneering a way for mass communication. He died in 2004 when he was 95.

How an early SigAlert caused traffic

Ironically, a SigAlert sort of created a big traffic jam.

Did you know?

  • Before Loyd Sigmon died, he was known to drive around in a cream-colored Lincoln Continental coupe with the vanity license plate “SIGALRT.”

  • The Santa Monica Pier’s bumper cars are also named after Sigmon’s work, dubbed Sig Alert EV. Their website says "Our Sig Alert EV is a great way to blow off steam after an hours-long commute to the west side"

In January 1956, a major train derailment happened — the Santa Fe train wreck — and an alert went out asking for any available doctors and nurses to respond. But so many people responded — including nosy onlookers — that it turned into an even bigger mess.

Priests, who were asked to come for spiritual help, were caught in traffic or turned away because of the amount of people driving over.

The derailment killed 30 people and injured 117. But the LAPD’s use of the SigAlert called into question exactly how effective (or ineffective) it was to broadcast such requests for help without a way to control the traffic build-up.

The L.A. Times put out an editorial days after the wreck that called out local authorities for poorly managing the emergency.

And while it praised how the SigAlert brought a swift medical response, the editorial board wrote that “nobody had the wit to stop” the onlookers on the highways.

What questions do you have about how L.A. works?

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How SigAlert Got Its Name (2024)


How SigAlert Got Its Name? ›

The term was originally the name of a pioneering system of automated radio broadcasts

radio broadcasts
radiodiffusion (plural radiodiffusions) (uncountable) The act of broadcasting by radio; transmission. (countable) A broadcast. › wiki › radiodiffusion
regarding traffic conditions, introduced in the 1950s and named after its inventor, Loyd Sigmon.

Where did the term Sigalert come from? ›

That the Sigalert was the brainchild of a broadcast pioneer named Loyd C. Sigmon. [At the time this article was written Mr. Sigmon was alive and well and driving a cream-colored Lincoln Continental with a hands-free cellular telephone and a vanity license plate that proclaim, "SIGALRT."]

Who owns Sigalert? › is owned and operated by iHeartMedia.

Who invented the Sigalert? ›

It was created in the early '50s by Loyd Sigmon, a radio executive at L. A's KMPC station. During the Cold War, civil defense officials were looking into how to make an alert system, a project that Sigmon developed.

What is a Sigalert in Los Angeles? ›

The official definition of a Sigalert is "any unplanned event that causes the closing of one lane of traffic for 30 minutes or more." Q. What is the origin of the term Sigalert? A. Sigalerts are named after an early radio engineer in Los Angeles, Loyd Sigmon.

How does Sigalert work? ›

A SigAlert is a notification system used by the California Highway Patrol to alert drivers about incidents that disrupt traffic flow, typically on interstates or major roads. Whenever a freeway is closed due to a crash – that's a SigAlert.

When was the Harbor Freeway built? ›

Is there a Sigalert app? ›

The Sigalert iPhone app is simple to use, but packed with information: *** MORE THAN JUST RED/YELLOW/GREEN - Sigalert offers incredibly detailed speed information. Sigalert's users know when traffic is moving 25 miles per hour and when it's moving 40 miles per hour.

What is LA rush hour? ›

Rush Hour. Los Angeles is like most other cities in the country regarding rush hour. Drivers traveling to and from work clog the roads between 7 a.m. and 10 a.m. during morning rush hour and between 4 p.m. and 7 p.m. in the evening. During these hours, the freeways are always jammed.

What time does LA traffic start in the morning? ›

Traffic: LA Rush Hour

Traffic is usually heavy on the freeways during morning and evening commutes when you're driving in Los Angeles. Weekday morning LA rush hour is roughly from 7 a.m. to 10 a.m. The evening LA rush hours are around 4 p.m. to 7 p.m. and later.

Why does traffic happen in LA? ›

Today, there are nearly twice as many registered vehicles in L.A. County as there are people. And, in a county covering 503 square miles, Los Angeles has about 650 miles of freeway. The many high-rise buildings that pack more office workers into relatively small spaces intensify the rush hour traffic in Los Angeles.

How to avoid traffic in Los Angeles? ›

How do you avoid rush hour traffic in Los Angeles?
  1. Avoid gridlock hours. This might seem obvious, but it's the main rule of moving smoothly around LA. ...
  2. Avoid the 405. ...
  3. Take alternatives. ...
  4. Use technology. ...
  5. Use public transportation. ...
  6. Go for a private car service.

Does the 405 go through LA? ›

Interstate 405 (I-405) is an Interstate Highway in the Orange and Los Angeles counties of California. It is a bypass route of the Interstate 5. It goes from the I-5 near San Fernando, through the west side of Los Angeles and Long Beach before ending back at the Interstate 5 near Irvine.

What is the traffic radio station in California? ›

Los Angeles, CA Traffic | 102.7 KIIS-FM.

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