It happened about 6:00 AM at Mile Marker-68 near Niceville.
The Florida Highway Patrol say 21-year-old Devin Brent Ellis Ferrante of Mossy Head was driving west on the interstate, when 49-year old Gregory Leon Curtis' tractor trailer rig hit Ferrante's pick-up from behind.
Both vehicles wound-up in the trees off the shoulder of the interstate.
A witness told troopers Ferrante was driving very slowly with his emergency flashers on, and that Curtis did not brake before the collision.
Paramedics life-flighted Ferrante to Sacred Heart in Pensacola where he is reported in very critical condition.