The drills are designed see how well the MBTA is equipped to deal with a security surge if there is a threat.

"It reads outside of bag, and if there is an explosive it will tell us what it is," said MBTA Deputy Chief John Martino said.

MBTA police already do random bag searches, but this drill is to prepare in case the Department of Homeland Security raises the threat level to orange.

"We've formulated a plan with the TSA to conduct more inspections, so we can cover more inspections when the alert level goes up," Martino said.

Anyone who refuses a bag check could be escorted off the property or arrested.