The MBTA is urging commuters to add 20 minutes to their expected travel times beginning Tuesday, as the agency prepares for frigid temperatures to impact service on bus, subway, and commuter rail lines.

“For us, our first priority is to run a safe system for all the riders and the employees that are operating them,” MBTA General Manager Luis Ramirez said Monday evening in a conference call.

The agency will be doing everything it can to maintain normal service, Ramirez said, but noted “given the last few days and the experiences we’re seeing across the region, we think it’s prudent to prepare” for possible delays.