Homeland Security Secretary Tom Ridge has asked train and rail operators to be on a heightened state of alert, noting the recent bombings in Madrid.

He said the Department of Homeland Security will develop a rapid deployment mass transit canine program trained to search for explosives in rail tunnels and will implement a pilot program this spring to test the feasibility of screening luggage and carry-on bags.

The department will also work with rail and transit leaders to encourage passengers to report suspicious activity in trains and stations, and will research new technology to detect and intercept attackers before they reach their intended targets, he said.

In addition to passenger trains, Ridge said in response to a reporter's question that freight trains carrying hazardous materials are "at the very heart of the discussion."

"We realize that's a vulnerability that could be exploited with potentially catastrophic consequences," Ridge said.