Metro plans to begin random searches of its riders’ bags in the coming days, the transit agency said Thursday, revisiting a plan first announced two years ago. Metro Police Chief Michael Taborn said the coordinated effort with the Transportation Security Administration was not in response to a specific threat but was part of a continuing effort to keep the system safe from explosives. Boston, New York and New Jersey transit officials do similar searches, according to the agency.

Metro officials would not specify when the first searches will begin, how long they will last, which locations will be targeted or how many riders’ bags will be searched. The agency planned to start alerting riders with pamphlets and station announcements on Thursday afternoon.