Metrorail Bottleneck
The biggest potential bottleneck in the Metrorail system lies in the narrow tunnel beneath the Potomac River through which Orange Line and Blue Line trains travel between Northern Virginia and the District. There is one track in each direction. A proposal that would build an Orange Line branch to Tysons Corner and Reston, would send additional trains through the tunnel.

BY NATHANIEL VAUGHN KELSO - THE WASHINGTON POST