Update: June 12
Metro plans to single track many lines weekday afternoons over the next 15 months to make repairs. A typical line would take about a month of weekday single tracking to complete. Paul Duggan has the story here in the Washington Post. The lines with the deepest and longest tunnels (Orange, Red) might get attention first. Other cities, especially New York, are likely to make similar repairs (but NYC usually has double tracks both sides in most populated areas).