In the wake of today's fatal and horrific Metro collision, both experts and WMATA are recommending commuters avoid Metro if possible. Commuters are also recommended to telecommute/web commute and stay home if possible.
Expect extended delays, even if you're coming from Virginia or Maryland, on the highways, smaller roads, and city roads. If possible (and sometimes it isn't) leave early or carpool. This is, of course, dramatically easier for the 9-to-5 crowd, and I find the constant drone for "everyone" to "stay home and telecommute" somewhat insensitive to people with less flexibility. (And I'm sorry. I wish we all had it so easy!)
Here's more detail from Get There, with an explanation of "why" ("It's only one line!") and what to expect:
The Red Line operates in the inner tracks and MARC on the outer sets of rails. The rescue and recovery effort spanned all four sets of tracks. The transit authority said that when the Metrorail system opens at 5 a.m. it expects to be operating a bus bridge service similar to what riders encountered in the hours after the crash. Trains probably will be operating between Glenmont and Silver Spring and between Shady Grove and Brookland. Riders could board the free shuttle buses connecting the stations. Bus shuttles can be quickly overwhelmed by demand. This will be a slow way to get to work.
Try to remain patient on the road. We're all in this together. Maryland police is currently "cracking down" on aggressive driving, so not only will it fail to alleviate the tangle in traffic, it can get you into serious trouble. (Which is an understatement, I know.)
Updates regarding today's collision will continue here. Re-routing information is here.