The long and short of it is that 83% of Metro's escalators are Westinghouse Modular 100s, a model discontinued 30 years ago. The Atlanta Rapid Transit Authority had an incident similar to but worse than the Rally to Restore Sanity incident in Washington, on New Tear's Eve 2007, in which 11 people were hurt.
The Atlanta Authority shut down most of the system's escalators (78% are Westinghouse Modular 100s) and determined that 56% needed repair work. This of course caused chaos with Atlanta Metro service. The effect of a similar shut-down in D.C. would be far worse as we have more than triple the number of total escalators and four times as many Modular 100s.
This article also points out a subject covered here on a number of prior occasions, Metro's inability to perform maintenance competently and timely without causing systemic chaos. For more go to: http://www.maryland-law.com/blog/metro-knew-about-escalator-braking-problem.cfm