A MetroAccess driver was arrested Friday by Metro Transit Police on charges that he sexually assaulted a disabled woman he was supposed to drive home.

Ezra Porter, 50, of Upper Marlboro, was driving the woman to her house on an April 19 trip that had been scheduled in advance with the transit service for people with disabilities. He stopped the vehicle in Bowie and "had inappropriate sexual contact" with her, Metro said.

The agency did not provide details.

Porter is charged with first-degree sexual assault.

A relative of the woman contacted Metro Friday afternoon to report the incident, Metro said, and Metro Transit Police investigated and then arrested Porter. Officials barred him from driving MetroAccess vehicles since the incident, the agency said.

Porter has worked for MV Transportation, which operates MetroAccess under contract, since November 2009. The company requires criminal background checks for all of its employees, but a company spokeswoman said she did not have information on whether Porter had a background check or whether Porter still works at the company. She directed questions to Metro.

MV Transportation's contract with Metro ends June 30. A group of five contractors will take over the service, with MV Transportation continuing to oversee the call center.

Porter is not the first MetroAccess driver to be charged with sexually assaulting his passengers. Three drivers for the service were implicated in sexual assaults in 2010, including one alleged rape. The company promised to retrain all of its drivers after those incidents.

The Americans with Disabilities Act requires Metro to provide MetroAccess service for people with disabilities that prevent them from taking Metrorail or Metrobus. But the service has had a problem with drivers quitting frequently. A report written by the Metropolitan Washington Council of Governments in 2008 concluded the service had a 111 percent turnover rate for drivers -- a figure more than triple the national average of 30 percent.

Many riders complain about poor service, and Metro officials have often been vexed by its high cost to the agency -- about $50 per ride.