Federal investigators are recommending that the federal government assume oversight of Washington's subway system, an unprecedented step for an urban mass transit system. 

The National Transportation Safety Board said Wednesday that the Federal Railroad Commission should take over safety oversight of Metro. 

The NTSB has been investigating an electrical malfunction that caused a train to fill with smoke inside a downtown Washington tunnel in January. One passenger was killed and more than 80 others were sickened. 

A regional committee currently handles safety oversight for Metro. The committee has no enforcement authority, and NTSB chairman Christopher Hart says that creates "an unacceptable gap in system safety." 

The NTSB says there's been little improvement in Metro's safety oversight since a 2009 crash that killed nine people.