They were rear ended by a semi-truck, and the injuries are described as serious but not life threatening:

Both Reid-Barringer and Reid were wearing seatbelts and were transported to Inova Fairfax Hospital in Falls Church. The driver of a 1997 Jeep Grand Cherokee and the driver of a 2007 Chevrolet Cobalt, also involved in the crash, were transported to the hospital with non-life threatening injuries.

“Mrs. Reid has a broken nose, broken back and broken neck. Lana has a neck injury and facial lacerations. Both Mrs. Reid and Lana are conscious, can feel their extremities, and according to doctors their injuries are non-life threatening,” Jon Summers, a spokesman for Sen. Reid (D-Nev.), said in a statement late Thursday afternoon.

One note here: Wear your damn seatbelts.