U.S. passenger trains are taking extra precautions in response to the terrorist attacks that killed or wounded more than 1,500 train riders in Spain. The attacks on Thursday have not prompted the United States to raise its terror alert, which is now at yellow, an elevated level, reported the Associated Press. Amtrak has increased patrols of its police force and canine units, spokesman Dan Stessel said. The railroad also intensified electronic surveillance of bridges and tunnels, and reinforced its message to employees to report suspicious activities to police. "[Amtrak] is continuing to review information received from the FBI and the Transportation Security Administration," Stessel said. Authorities in New York have also increased security in city subways and commuter trains, including using bomb sniffing dogs, reported the AP.