On the eve of federal safety hearings into Metro’s deadly June 22 crash, four senators sent a letter to Metro warning that federal officials will intervene if the transit agency does not improve its “unacceptable” safety record.

“Such a pattern cannot be viewed as a string of isolated ‘accidents,’ rather, it is clear that there is an institutional failure,” said the letter from Senate Banking, Housing and Urban Affairs Committee Sens. Chris Dodd, D-Conn., Richard Shelby, R-Ala., Robert Menendez, D-N.J., and David Vitter, R-La.