In this undated photo provided by the Los Angeles County Metropolitan Transportation Authority, stand-off explosion detection units, left, are deployed in a corridor at The Metro in Los Angeles. U.S. Sen. Chuck Schumer, D-NY, wants the Transportation Security Administration to speed up plans to equip transit hubs with the screening devices that can detect suicide vests like the one that exploded in a New York City subway tunnel on Dec. 11, 2017.