Every major metropolitan area has it's highway information system. Californiahas Sig alerts. A "Sig Alert" is 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." Sig Alerts are carried on radio, television, highway message signs, and posted on their Web site. The actually made it into the dictionary in 1993.
Los Angeles radio stations began carrying traffic information early on. There were 74 million cars in the United States by 1960. We got there very quickly. There were only about 4,000 in 1900 and less than 200 miles of road were even paved. large cities led the way, so they also had the curse of leading in traffic, gridlock and car wrecks. [ref hypertextbook] The anecdotal version is that people began calling the police department, soliciting traffic information. I cant corroborate thsi at all. What is certain is that it was Sigmon who convinced the L.A.P.D. to call KMPC-AM when accidents were effecting traffic. KMPC summarized all this in regular traffic reports. Sigmon thought it woudl be good for ratings. He was right. More here.
LAPD's chief, William H. Parker who later insisted they be called "Sig Alerts" was also the person who insisted that KMPC not have a monopoly on the information. But the stations that participated also had to use the specially made Sig Alert reel-to-reel decks. The words Sigalert" were stenciled on the side. In 1969, the Calofirnia Highway patrol assumed responsibility for freeway traffic from the LAPD and also the mantle of control over sig alterts. They worked to expand it state wide. Messages are still broadcast on the current CHP frequency - 42.34 MHz. But the information is mroe commonly acquired directly from the CHP's website. Loyd C. Sigmon died in 2004. He was 95 years old.