Metro said its transit police arrested a 50-year-old MetroAccess driver after he allegedly sexually assaulted a passenger.

Ezra Porter of Upper Marlboro was charged with first-degree sexual assault.

The incident occurred on a MetroAccess vehicle April 19, according to Metro officials. Porter allegedly stopped the vehicle in Prince George’s County and had “inappropriate sexual contact with the adult female victim prior to transporting her to her residence,” according to a news statement Metro issued Wednesday.

A family member contacted the transit agency’s police department Friday, and Metro said an investigation was started. Metro spokesman Dan Stessel said he is not releasing the victim’s age because of privacy concerns.

Porter has been a driver for MV Transportation, which has a contract with Metro to provide shuttle service for disabled riders, since November 2009.

In March, Metro awarded an $86 million contract to five vendors, including MV Transportation, to run various parts of its door-to-door shuttle service for disabled riders.