The History of the Sigalert and How It Changed Traffic Reporting

The History of the Sigalert and How It Changed Traffic Reporting began in 1955 in Los Angeles, California, when a radio executive named Lloyd Sigmon invented a system to quickly broadcast emergency alerts to the public. Today, the term "Sigalert" is officially used by the California Highway Patrol (CHP) to define any unplanned traffic event that blocks one or more lanes of travel for 30 minutes or more. By establishing a direct communication link between law enforcement and radio broadcasters, the Sigalert revolutionized how drivers receive real-time road information, paving the way for modern traffic reporting. ## The Origin of the Sigalert In the mid-1950s, Los Angeles was experiencing rapid suburban growth and a massive increase in car ownership. Lloyd Sigmon, an engineer and co-owner of the KMPC radio station, wanted a faster way to obtain breaking news and traffic information from the police. At the time, reporters had to manually monitor police radio frequencies or wait for official press releases, which often delayed critical updates. Sigmon developed a specialized radio receiver that could be installed at local radio stations. The receiver remained silent until the Los Angeles Police Department (LAPD) dispatched a high-priority bulletin. To broadcast an alert, the police dispatcher would transmit a unique, sub-audible tone. This tone triggered the receiver at the radio station, activating a red light and automatically recording the police dispatch on a tape machine. Radio hosts could then broadcast the warning to their listeners within minutes.

Updated July 24, 2026 3 min read 564 words

## How the System Got Its Name When Sigmon proposed the system to LAPD Chief William H. Parker, Parker recognized its potential to clear congested roads during emergencies. The LAPD officially adopted the technology in September 1955. Chief Parker decided to name the broadcast alert system after its creator, calling it the "Sigmon Alert." Over time, the name was shortened to "Sigalert." The system was initially used not just for traffic accidents, but for any major public emergency, including gas leaks, train derailments, and urgent requests for off-duty doctors to report to hospitals. ## Changing the Landscape of Traffic Reporting

Before the Sigalert, drivers had no reliable way to learn about road conditions ahead of time. The invention of this system changed traffic reporting in several key ways: * **Real-Time Communication:** It bypassed traditional news-gathering delays, establishing the first direct, automated pipeline between emergency services and the public. * **Driver Behavior Modification:** For the first time, motorists could hear about a major bottleneck while driving and choose alternative routes, reducing secondary collisions and clearing the way for emergency vehicles. * **Standardization of Traffic Alerts:** It set a precedent for how government agencies and media outlets collaborate to manage highway congestion. As the California highway network expanded, the California Highway Patrol took over the administration of the alert system. The CHP standardized the criteria for issuing a Sigalert to keep the notifications meaningful and prevent driver alert fatigue. ## The Modern Definition of a Sigalert

Although technology has evolved from analog radio receivers to digital mapping applications and GPS navigation, the Sigalert remains an official term in California. The CHP continues to issue Sigalerts when specific criteria are met. Currently, a Sigalert is declared when a traffic incident blocks one or more lanes of a freeway for at least 30 minutes. These alerts are automatically pushed to traffic reporting services, digital highway signs, and navigation apps, ensuring that Lloyd Sigmon's 1955 invention continues to influence how millions of commuters navigate the roads today.

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