Serious ouch. Interestingly it looks like a case of late hard braking. The trailing driver was clearly not paying attention.

That's a horrible accident. I feel for the guy.

Reminder: don't follow cars too closely, not because you wouldn't be able to stop in time, but so that you can slow down more gradually and give the car behind you time to wake up and take notice.

Of course, that's pretty much impossible on the DC area roads and beltway during rush hours. Wear hi-viz gear.