If a truck was pulling a trailer at 60 MPH with a ramp down on the
road. Could a car be loaded on the trailer which is going 60 MPH, if 
the car was traveling in the same direction at a faster speed, up on
the trailer?
Or would the car get on the trailer and crash through the front of the trailer?
Or could the car stop while on the trailer, which is being pulled at 60 MPH?

I found documented evidence that this stunt has been accomplished at
40 MPH.  Depending upon the length of the trailer and the amount of
friction between the car's wheels and the trailer's surface, the
vehicle would either be stopped on the carrier or would crash through
the front of the trailer if it were performed at 60 MPH.  As a stunt
driver notes, braking as hard a possible but avoiding skidding is of
critical importance.  This stunt was performed at 40 mph in an episode
of Fear Factor.  The Chevrolet SSR advertisement in 2004 "Car Carrier"
shows multiple examples of this stunt, also.  It was available for
download at the Chevrolet website at
http://www.chevrolet.com/library/commercials/, but it is no longer
available.  One source maintains the cars in the commercial were
actually backed off of the carrier, but Tony Vella, a stuntman,
maintains they were not and describes how it was done.

Sources:

"No trick photography here......its all what you see, only the
vehicles are not traveling as fast as they appear....film has a
tendancy to make things appear faster than then are. However it is
still just as dangerous and requires expert timing. It's a matter of
approach, the vehicle going onto the ramp must equate,and then
actually  [SIC accelerate] a little faster than the carrier for this
to work to gain access. Then once the rear wheels have cleared, Yes,
the vehicle must threshold brake quickly to stop ( braking without
skidding )."

"Drive a Car onto a Moving Car Carrier" J Fudge.com (January 21)
http://www.jfudge.com//modules.php?name=News&file=article&sid=150 
Provides an explanation by stuntman Tony Vella of how this stunt is
done.

"GM's An American Revolution Car Carrier Commercial"
http://impalassforum.com/cgi-bin/ultimatebb.cgi?ubb=reply;f=8;t=007352
 Provides information about where to download the Michael Bay-directed
Car Carrier commercial.  Unfortunately, the links are dead.

"Contestants would start out driving a car next to a moving car
carrier going 40 miles per hour. When a horn sounded, they would have
to drive their car up a ramp and into the back of the car carrier. The
contestant to do this the fastest would be the Fear Factor Champion."

"37. Dog Attack; Gas Chamber; Car Carrier Drive-Thru" Stunt #3: Car
Carrier Drive-Thru" TV.com (2006)
http://www.tv.com/fear-factor/show/4674/episode_guide.html&season=3

"Stunt #3: Car Carrier Drive-Thru
Chad was first. He did the stunt with no problems and got a time of 10
seconds. Kate was next. She also did not have any problems, but her
time was 13 seconds. Kate was eliminated. Brandy was last. When she
was pulling in, her left rear tire went off the ramp and she got
stuck. Chad was the Fear Factor Champion."

"Dog Attack; Gas Chamber; Car Carrier Drive-Thru (episode #37)" TV.com
(2006) http://www.tv.com/dog-attack-gas-chamber-car-carrier-drive-thru/episode/216933/recap.html

"A New Campaign From Chevrolet" By ELLEN PILIGAN, The New York Times
(December 19, 2003) http://www.nytimes.com/2003/12/19/business/media/19adco.html?ex=1137733200&en=fe53e827a891d61e&ei=5070

"The ad is a trick. The cars are being driven OFF of the trailer, then
the [SIC video] is shown backwards with careful editing.

Still, kinda cool though."

"Neat Commercial" by stu norman (1/2/04)
http://www.classicalpontiac.com/qa7/display.cgi?directory=topics&number=52026&title=Neat+Commercial&.
 I could not locate any material confirming his claim.

Some information on the physics of automobile braking:

"How To Stop In An Emergency Without ABS" Canadian Direct Insurance
(2004) http://www.canadiandirect.com/Renderer.jhtml.88.html

"Stopping Distance For A Vehicle" CSG (2006)
http://www.csgnetwork.com/stopdistcalc.html

"The net external force stopping a car comes from the friction force
between tires and pavement. Stopping a car with ordinary brakes may
result in wheel lock; that is, the wheels lock in position and are not
able to rotate. When this happens, the tires skid and the coefficient
of kinetic friction determines the braking distance. Cars equipped
with an antilock braking system (ABS) have a sensor that releases the
brake pads the instant the wheel locks up. After a brief pause the
brakes are then quickly re-engaged. If they don't lock up again, all
is well. If they do, the ABS releases the brake pads again. This
processes can repeat many times a second. In any case, the tires are
not allowed to lock for more than a few milliseconds. The car is then
stopped using the force of static friction alone."

"Friction" by Glenn Elert, The Physics Handbook (2005)
http://hypertextbook.com/physics/mechanics/friction/

Sincerely,

Wonko

Search terms: SSR "car carrier" download; driving car onto moving "car
carrier" stunt; friction braking distance; "threshold braking"

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Request for Answer Clarification by r7w7h7-ga on 18 Jan 2006 13:09 PST

Would it depend on how long the trailer was. Would it make a
difference if you acclerated and before hitting the ramp, than placed
the car in neutral such that the wheels would not be turning, or
acclerating.
What would the max speed be for the car to accomplish this act?

What about the trailer is moving at 40 MPH, the car would have to be
going atleast 41 MPH, that is a total of 81 MPH, how could it stop on
a small trailer?
Thanks randy head

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Clarification of Answer by wonko-ga on 18 Jan 2006 20:44 PST

The issue is one of frames of reference:  the car is moving at 41 MPH
relative to the ground, but as soon as it is on the car carrier's
ramp, the frame of reference changes to the car's speed relative to
the ramp.  At that point, it is only 1 MPH faster, so slowing down the
car is not particularly difficult provided one avoids skidding. 
Skidding not only increases the stopping distance, but it makes it
impossible to steer the car (which is probably the more dangerous
consequence if the speed differential between the car and the car
carrier is small).

Sincerely,

Wonko

yes you can do this, what happens once it is on depends on how quickly
you hit the brakes.

r7w7h7-ga: Don't add 41 and 40 to 81 , that's wrong. If I take your
example figures, the relative speed difference between the truck and
car is only 1 MPH, so the car can get up the ramp and then just needs
to slow down only 1 MPH to come to a halt on the truck. The issue is
with the wheels only: they will be spinning at 41 MPH and when they
get on the truck the'lll have a surface under it at zero speed, so it
will give the car an extra acceleration forward. If the car is in
neutral when hitting the ramp, then the acceleration effect will be
minor as the stored energy in the wheels is small compared with the
weight of the car goiing upward on the truck. The effect can be
compared with the following situation: Imagine you drive over a really
icy patch on a road, and slightly hit the break on a car without
ABS.... as a result the 4 wheels will lock up, and your speed
indicator will show 0 MPH. Imagine then that you release the break at
the time you're back on the non-ice road with good friction. suddenly
your wheels will start spinning again , the rubber will suffer a
little bit maybe, but asa long as you stayed on course, your car will
continue at roughly the same speed.
Going back to your example: As the speed diffrence between the truck
and car is very small, the inertia of the spinning wheels will not
cause much difficulty.
Timing still is important though, as getting up the ramp without
beeing in neutral will also add the inertia of the whole motor.
Hope this explains... 
Peter

Wonko, great research!
Even I have seen a film on TV with this scene.  The ramp also helps
break the car's speed, and the car can start to slow down before it
hits the ramp.
Theoretically, the stunt should be possible at 60 mph, or even higher
speeds, since the significant factor is not the absolute speed but the
difference between that of the truck and that of the car; if it works
at 40/41, then it would work at 80/81, but it would tax the car
driver's skill and be more dangerous.
Easier to speed up the film of the scene in the movie.

I don't agree with Tdniktdeog, the truck's ramp is not at zero speed,
that is the roadbed.  The truck and ramp are moving just a bit slower
than the car, which does not have to break its momentum to zero but
only to that of the truck.
That is the important consideration.

Okay, this may correct my above statements, since at higher speeds,
the moment will be greater, perhaps despite that fact that the
difference in speeds is the same (dunno).

For a film, the closing speed relative to the overall speeds is
significant.  If the closing speed can be 5 mph, at 40/45 this looks
dramatic; at 80/85, the scene of the closing is drawn out.

Nice question. I've seen this one mentioned with the airplane on a
moving runway question. I wish i had gotten here sooner :-)

If the trailer is moving at 40 mph and the car at 41 mph, when the
car's wheels come up on the ramp of the trailer they will still be
rotating at the same rate they were when they were on the road.  The
car lose some momentum when it hits the ramp with a bump.  It will
lose some more momentum from the upward grade of the ramp, and finally
some additional momentum will be lost to the extent the wheels slip
when they come up onto the ramp.  But to the extent the wheels grip
the ramp, the car will gain momentum and lurch forward on the ramp. 
Perhaps it will retain, say 25 mph.  The car would then be going
forward at 25 mph on the ramp (65 mph relative to the ground) and the
driver would have to hit the breaks quickly and firmly to stop in
time.

What about front-wheel-drive vs. rear-wheel-drive vs. all-wheel-drive?

May I add another variable - for the pleasure of watching you all
field it? In the original 'Italian Job' film the cars were front wheel
drive. To heighten the tension there were a couple of failed attempts
which led to a car running backwards down the ramp.  With the front
wheels on the ramp and the rear wheels on the road, the two sets of
wheels were rotating in opposite directions. This means that the
wheels had to perform a near-instantaneous change of direction where
going from ramp to road.  Would this rule out a permanent four wheel
drive vehicle even if it were in neutral or the cluch were depressed?
I guess you could only roll off the ramp; being in reverse gear would
be disastrous!