Yesterday's accident represents, first a major blow to Metro's corporate pride. Metro has always been proud that it relies on computers, not human operators, to control its trains. As with many aspects of Metro, the party line has always been that the transit systems that existed before Metro were inferior and that Metro's highly engineered approach represented a significant step forward. Folks who have used the New York or London systems on a regular basis may not be completely convinced. Stairs, for example, don't break down nearly as often as escalators. Nonetheless Metro's future is tied up with heavy reliance on automated signaling systems.
Metro is counting on its signaling system to allow it to accommodate more trains through the Roslyn tunnel. When Dulles rail goes into operation, its trains will share the Roslyn tunnel with Blue and Orange trains. To reduce congestion at Roslyn, Metro has suggested diverting some Blue line trains to the Yellow line, allowing them to cross the Potomac via the Yellow line bridge. It remains to be see whether this proposal will be implemented. The other option is to reduce the headway between trains. Metro now allows something like six minutes between trains. Allegedly trains in Japan operate with one or two minutes headways. Some have suggested that Metro could reduce its headways to three minutes, more or less doubling the number of trains possible on any stretch of track, particularly the Roslyn tunnel.
Reducing headways is possible only by relying still more heavily on automated controls. If Metro loses faith in its current system or, perhaps more important, if the public loses faith in it, Metro will have to find a better system or be content with running with the current headways. Finding a better system would probably not be easy or swift. Retaining the current headways will limit the number of trains Metro could run on Dulles rail. Somehow, I doubt that potential customers will ride Dulles rail if trains run only every 15-20 minutes.
The real solution has always been digging a second Roslyn tunnel and expanding the Orange line from two tracks to four. -- a proposition even more expensive than building Dulles rail, but vitally necessary. Perhaps someone ought to ask Ken Plum and the other Dulles rail advocates how soon they plan to fund the needed expansion.
