The company that operates the MetroAccess service has authorized an independent investigation into its practices.
MV Transportation is the sub-contractor operating Metro's shared-ride door-to-door service for disabled people unable to use buses or rail.
Recently four MetroAccess drivers have been accused of sexually assaulting passengers.
MV has initiated an independent inquiry to look at the company's hiring and training practices.
MV already conducts background checks and operates a 110-hour training program for new employees.
"The inquiry will look for ways that maximize passenger safety that go beyond any applicable standards," said Patrick Reilly, the former Federal Transit Administration Chief Counsel who's been appointed to lead the investigation.
Reilly said the findings will help MV determine how it can go beyond its legal responsibilities and provide additional protections to passengers.