WASHINGTON -- The Homeland Security Department lowered the terror threat level Friday for the U.S. mass transit systems, effective after the day's rush hour.
Homeland Security Secretary Michael Chertoff said he would end the high alert for city buses, subways and trains after 36 days of being at code orange in response to the deadly July 7 rush-hour bombings in London.
His order -- effective at 8 p.m. local time Friday -- was returning the national mass transit threat level to code yellow, signifying an elevated risk instead of the high-alert orange.
"While we are changing the threat level at this time, we continue to urge state and local officials, transportation authorities and the general public to remain alert," Chertoff said in a statement. "Public vigilance is very important, and we encourage all citizens to keep a watchful eye for items left unattended or suspicious behavior and report any incidents to local authorities immediately."
Despite no specific, credible evidence of a threat against the United States, authorities raised the alert last month as a precautionary measure against any copycat attacks inspired by the bombings of three London subway lines and a bus.
A total of 56 people, including four suicide bombers, were killed in the London attacks. U.S. officials extended the orange alert after follow-up attacks in London two weeks later, on July 21.
However, Chertoff said, authorities will continue closely monitoring threat intelligence for any indication of an attack, as "we are also aware that the London and Madrid bombings were conducted without warning."
A March 11, 2004, attack on the Madrid commuter rail network killed 191 people and wounded more than 1,500. Islamic extremists claimed responsibility for the bombings on behalf of al-Qaida and in revenge for the presence of Spanish troops in Iraq.
The monthlong alert in the United States targeted only mass transit systems, and marked the seventh time the terror threat advisory level had been raised to orange since it was created in 2002.
Maintaining security at orange alert levels -- with increased police patrols, heightened inspection and surveillance and the use of bomb-sniffing dogs -- costs mass transit systems an estimated $900,000 a day.