Two major Bay Area transit agencies are remaining vigilant, but have not implemented any extra safety measures as federal investigators probe an alleged terrorism plot to detonate bombs in the United States.

Federal agencies have arrested two men in Colorado and issued bulletins to police and transit agencies across the nation advising extra cautionary measures as the investigation continues.

BART spokesman Jim Allison said the agency received a notice from the U.S. Department of Homeland Security on Friday. Most of the recommendations, such as patrolling stations, trains and platforms, are already part of BART security measures, he said.

The only recommended measure BART does not practice is random bag searches, Allison said. With 335,000 people riding trains each day, such a measure would be unlikely unless the national terror alert were raised to red, he said.

However, Allison also allowed that BART does not always inform the public when it increases security.

“There are certain strategies and tactics that we would not want to tip our hand to,” he said.

Allison also declined to discuss whether BART has received any specific information on threats to the system.

The agency remains aware that “BART has been listed as a potential target in the past,” he said. “We are important to the region and therefore a target.”

Muni spokesman Judson True also said his agency does not provide information on specific security threats.

While Muni is not stepping up any security activities, “we continue to remain vigilant about security on the system,” he said.

This includes K-9 patrols and regularly sweeping vehicles for suspicious packages.

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