Washington (CNN) -- The United States is replacing its much-mocked system of color-coded terrorism alerts with detailed advisories about specific threats, Homeland Security Secretary Janet Napolitano announced Thursday.
"When we have information about a specific, credible threat, we will issue a formal alert providing as much information as we can," Napolitano said. That information will include a summary of the threat, steps authorities are taking to guard the public and what the public can do, she said.
"The alerts will be specific to the threat. They may recommend certain actions or suggest looking for specific suspicious behavior. And they will have a specified end date," Napolitano said in a speech at George Washington University.
Napolitano's formal announcement confirmed reports that emerged Wednesday. The new system, set to take effect in late April, replaces the five-color system established after al Qaeda's September 11, 2001, attacks on New York and Washington.
Napolitano said those warnings were "too often accompanied by little practical information." The new system, she said, is built on the idea "that we are all in this together, and that we all have a role to play."
The five-color system has rarely changed from its middle setting of yellow, or "elevated," for the general public and orange, or "high," for commercial aviation. It has not been lowered below those levels since its establishment in 2002.
The system was the butt of jokes and parodies almost from the start, and polls found that the public considered it confusing. Kate Hanni, of the airline travelers' advocacy group FlyersRights.org, called it "very useless."
"People just ignored it," Hanni told CNN on Wednesday. Since the color rarely changed, passengers came to believe it didn't mean anything, she said.
In addition, some critics accused the Bush administration of manipulating the system to gin up fear at politically sensitive times. Just days after he announced his resignation in 2005, then-Homeland Security Secretary Tom Ridge told a Washington forum that he sometimes disagreed with the rationale for raising the alert but was overruled by others on the administration's Homeland Security Advisory Council, which made the decisions. The Bush administration denied Ridge's assertions.
Napolitano said the new system "is built on a clear and simple premise: When a threat develops that could impact you -- the public -- we will tell you."
The alerts will distinguish between "elevated" and "imminent" threats and could be limited to warnings for specific industries or police or communicated more broadly to the public, she said.
The yellow alert was raised to orange five times for the nation as a whole and three times for specific industries. The orange alert for aviation was raised to red once, in August 2006, and only for flights from Britain to the United States.
The alert followed the announcement by British authorities that they had disrupted a major plot to blow up jetliners, and it was lowered back to orange six days later.