if you fall from the back of a moving vehicle at highway speeds do you
roll the same way
as the vehicle is moving or the opposite on inpact

Same way, 'cuz that the direction you are already going, and pretty fast.

I hopped off the back of a moving station wagon tailgate once and
learned an important physics/relativity lesson.

If you literally just fall off the back of a moving car, in other
words you just slip off, making no effort to shove off and negate any
of the car's speed, then you'll land on the pavement moving at the
same speed as the car. Thus, the side of you which comes first into
contact with the road will be subject to frictional drag. The part of
your body scraping against the asphalt will lose speed even as the
opposite side persists onward due to its inertia. So your top & bottom
will be traveling at different velocities, the top moving forward
faster than the bottom. You'll quickly end up rolling in the same
direction as any of the wheels of the car off which you just fell.
(You'll also get pow'rfully hurt!)

   But let's say that you are uncommonly strong. You might then shove
off the rear of the car, accelerating away from it. If you shove off
hard enough you'd subtract from your speed that of the car, and land
with zero speed relative to the road surface. If you were even a lot
stronger, you could subtract more than the car's speed relative to the
road, giving you the velocity of a car traveling in the opposite
direction. In that case, you'd roll in the other direction.

   Don't try any of this. :)

Qed100, shoving off at about 30m/s? Human muscles aren't capable of
such acceleration, the bones they attach to aren't strong enough for
such stresses, and the joints cannot resist that much motion. I expect
there's a state law against it as well. If not, this is something that
should be taken up with the local legislature. Beats selecting a state
legume...

I was the one watching Lee Majors with my 10 year old peers and
saying, "But it really can't be done" and getting pillows thrown at
me.

"Qed100, shoving off at about 30m/s?"

   Indeed. That's why I proposed, "But let's say that you are
uncommonly strong." At highway speeds, one would be very uncommonly
strong, even to the point of being unhuman! :)

In my youth around Dublin, Ireland they had double decker buses with
an open platform at the back with a vertical pole in the middle of the
platform at the edge. It was common practice to lean out holding the
pole and drop off the bus while it was still moving as it slowed for a
stop. In order to survive this unscathed you had to judge exactly the
right moment to drop. To early and you rolled base over apex in the
direction of the bus to late and you were subject to the derision of
your mates.
Get it right and you had to run really fast in the direction of the
bus avoiding people and street furniture. The slap of your second foot
to hit the ground actually hurt!