Hope it's not real...
Good film editing though and what makes it work is the build up to it.
Here's how you can do it.
At 0:39 the camera is stationary shooting one angle. 2 shots are taken.
1) the girl running into the street, then bending her body and falling.
2) CUT
3) 2nd shot of car alone on street driving into frame coming to a stop
editing:
1) a frame from shot 1 is edited (photo shop) or cropping tool in video editor and background is taken out
2) shot 1 is layered over shot 2 and key framed to move with the direction of the car
3) Voice of roommate overdubbed (or taken from 1st shot)
0:40 final scene, camera back in motion.
An alternate way to edit is to:
1) cut a frame of the girl hunched over the car, cut the background out, and keyframe the shot in motion overlaying the background. To make that realistic, you'd also have to overlay the cars tires and rims in motion on the cut out / motionless frame.
Last option is using a green screen (which they didn't)
All of this has to be planned out and shot in a short period of time to keep the natural scenery, lighting and weather conditions consistent. (or there'll be lots of time color correcting etc.)
Pause the video and drag the player, to see it.
Here's a vid on achieving this:
How to Make the Hit By a Car Special Effect Video ? 5min.com
If they didn't do this... and its real, that's the shits........