WASHINGTON (AP) _ The Secret Service says it has expanded its security perimeter around the White House following the explosions at the Boston marathon. Secret Service spokesman Brian Leary says the perimeter was expanded out of an abundance of caution, and it’s not unusual for the agency to expand or contract security perimeters. Metropolitan Police, meanwhile, say the department is on heightened security status, but did not provide any further information. And Metro Transit Police say they have ordered all day shift patrol officers to stay on duty through the evening rush. In Maryland, Prince George’s County Police say they have increased security at all critical infrastructure in the county. Baltimore officials also say public safety agencies have moved to a state of heightened awareness.