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What Is a SigAlert?

By Holly Collins
Updated May 23, 2024
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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.”

What Does Sig Alert Mean?

When a SigAlert is issued, you can almost always guarantee a significant traffic jam in that area. Not only is this caused by the original incident, but emergency vehicles occupy additional areas of the road, cars need to merge out of the closed lanes, and people tend to slow down and look at the accident as they pass by. All of this contributes to a long and slow commute. If you hear that a SigAlert is in effect, it means you should pay close attention to where the problem is at and do your best to avoid it.

How Do SigAlerts Help Drivers?

If you live in a large city that utilizes the SigAlert system, it’s always a good idea to check for closures before you leave for home or work. Whether you sign up for text alerts, check the local news website or listen to the radio, you have many options for checking traffic before you hit the road.

Shorter Commute

If a SigAlert is issued, it gives you time to figure out an alternate plan. You can evaluate a map to determine another route, leave for your destination earlier or wait until the traffic has cleared. It’s also great because you can notify loved ones or childcare providers if you run late due to the extended driving time.

Driver's Sanity

Sitting in a major traffic jam is not high on anyone’s list. Long delays are stressful and require a driver to pay close attention for an extended time. This experience can cause drivers to become anxious, frustrated and tired, none of which helps a driver get home safely. SigAlerts makes it easy for drivers to avoid the gridlock and get home without unnecessary frustration.

Driver's Safety

Encouraging drivers to avoid high areas of traffic also keeps them safe. Since most rear-end accidents happen during times of dense congestion, avoiding this situation may prevent other fender benders. Not only does this prevent injury and property damage, but it also allows first responders to focus on the initial collision and not get pulled away to assist with the fender-bender.

Improved Traffic Flow

When a large percentage of drivers take alternate routes to avoid the jam, it also makes less congestion in the collision area. This means that the gridlock can clear up faster because fewer cars are in the area.

What Are Common Incidents That Cause a SigAlert?

Anything that blocks a lane of traffic may cause an alert. Frequently, this is caused by a crash between one or more cars. Many vehicles are constantly on the freeways in large metropolises like Southern California. They travel too close together at speeds that prevent drivers from stopping in enough time to avoid an accident. A collision involving a single vehicle, multiple cars or traumatic injures may each prompt a SigAlert.

Do SigAlerts Always Indicate That There’s a Collision?

Even though collisions are the most common cause of SigAlerts, there are other reasons they can occur. Some examples are:

  • Brush or structure fires
  • Dangerous debris
  • Overturned train cars
  • Police or criminal activity
  • Hazardous material spills
  • Pedestrians on roadways
  • Flash flooding
  • Mudslides

Law enforcement and first responders have some discretion when declaring a SigAlert. If a lane is blocked for any reason, they can report an alert to keep drivers away from the area.

How Often Are SigAlerts Used?

In large cities with millions of drivers, it’s not surprising that there may be a SigAlert every day. When the weather is terrible, there can be multiple areas of extreme traffic simultaneously. On average, there are over 2500 alerts broadcast every year in the greater Los Angeles area. With this many severe incidents, it’s easy to see that checking road conditions before traveling is always a good idea.

How Long Does It Take To Clear a SigAlert?

There is never a guarantee that an incident can be cleared within the estimated amount of time. While law enforcement may make an educated guess as to how long the driving lanes will be closed, things can change at any point. Fortunately, officers can extent SigAlerts if cleanup takes longer than expected and cancel them if crews get things cleared faster. Once crews clear the lanes, the alert is allowed to expire or is canceled, and first responders leave the scene. While the lanes reopen, there may still be a lot of congestion on the road until the traffic flow improves.

WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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