Thousands of commuters continue to breathe high levels of lung-damaging diesel exhaust at Chicago’s Union Station, in part because of nagging maintenance problems at the Old Post Office that straddles the southbound tracks.

Testing by Amtrak has determined that ventilation fans at the shuttered post office building repeatedly malfunction. At times, the system of 11 ducts and fans has operated at just 53 percent of its design capacity, according to a letter to U.S. Sen. Dick Durbin from Joseph Boardman, Amtrak’s president and chief executive.

Read more at the Chicago Tribune.