[brasso]

And possibly then being hit by (multiple) other moving vehicles in with the bargain...

[ScytheKnight]

To me sounds more like an Edge roll... it's the sort of thing you're probably either going to survive relatively unharmed, a complete mess, or a splatter.

[Fizzygoo]

I would go with:

Getting thrown out of a moving vehicle means the victim, in their rage at being thrown out of the vehicle, has decided to try and ram the Earth through a combination of their momentum and gravity.

Determine the speed the vehicle was moving when the character is thrown out to determine base damage (SR5, pg 203).

If the victim wants to put more oomph into their attack against Gaia, they could make a Vehicle skill + Reaction as the attack (as per ramming rules pg 203), but since they are the vehicle it's a GM call on whether to let the victim, now essentially Attacker (of Earth), roll Body + Reaction or Free Fall + Reaction or just a Reaction -1 die. All of which equates to the attacker decided to headbutt the pavement dress-strap of Earth's human-made evening ware which I would gladly add some extra damage dice to. Of course the planet technically gets a Reaction + Intuition test to get out of the way, but its Reaction is pretty damn slow most of the times and its Intuition is off the hook (according to this couple down the street selling various plants and what not) and its Body...well, she has the soak dice to take nukes and keep on rolling, probably not going to worry about a meatbag going plop on the roadway.

Most Attackers won't want to try and sucker punch the street on their way down as it will increase the damage they deal to Mother Earth and half of it is applied to themselves, rolling Body + Armor - 6 AP to resist.

So getting thrown out of a vehicle moving at 100 m/CT (75 miles per hour) means the attacker will be attacking the ground with a base Body x 2 damage rating which they take half of.

One might expect a bit more *splat* at 75 miles an hour, so the GM could double the end result damage before the resistance roll or what not. But I'm no biologist.

The other way to go is treat it as falling damage.

Characters fall 50 meters on their first CT (SR5, pg 172)
So if the vehicle is traveling at 100 meters per CT, and the character "steps out" at 1 meter height, they will travel 2 meters forward (x speed is twice that as y speed, and only gets to travel 1 meter before hitting the road).

For big splat just say those 2 meters forward was a very pleasant flight, but then you hit the ground and soak the remaining 98 forward meters/turn (the down doesn't count, as you were building up to 50 meters/CT and only made it 1, but you started out going at 100 meters/CT along the road and now have to stop because of, well, road). So it's the equivalent of falling for about  1.3 Combat Turns, ignore the first 3 meters, and the character takes 95 boxes of physical damage resisted with Body + Armor - 4 AP.

Option A seems more cinematic.
Option B seems more TPK-Happy.
Option C we can't discuss.
Option D use Option A but don't halve the damage to the "attacker"...and maybe add +1P per 10 meters/CT the vehicle is moving at before relieving itself of unwanted cargo.
Option E use Option B but divide the damage by the failed-at-life runner's Body, round down. So big Body troll might have to resist 9 to 13 boxes (95/Body of 10-7) while skinny little technomancer recluse will be taking all 95, or maybe 47 boxes.
Option F something else?

[Herr Brackhaus]

Using the fallling damage rules seem the most appropriate to my mind.

That being said, speaking as a motorcyclist who've walked away unscathed from two lowsides at over 100mph, one highside at around 60mph, and a car attempting to make a u-turn through me and the bike while I was going approximately 20mph, I'd say that the proper gear most definitely makes a difference.

EDIT: Revised opinion.
While roadrash is a real possibility of falling out of a moving vehicle, what's likely to really damage you is sudden deceleration (i.e. crashing into something while at speed).

Given this, I would treat exiting a vehicle at speed as a crash, with the following modifications (houserule terriority).

1. The fall itself does not cause any damage unless it occurs above the threshold for which falling damage kicks in (3 meters for most characters, meaning the character would have to fall from a heigh of at least 4 meters for any falling damage to be applicable in most cases)
2. The character rolls Gymnastics + Reaction* (Speed), where Speed is that of the vehicle the character just exited
   2a. If this test is successful, the character takes no damage from skidding along the ground
   2b. If this test is unsuccessful, the character must resist a DV of (Speed * 2)P, where once again Speed is that of the vehicle the character just existed
3. The character arrives at a stop at the end of the combat turn in which he exited the vehicle, having moved a total distance of half the Walking Rate of the Speed he exited the vehicle
   3b. If anyone tries to ram the character while he is still moving, they take a -3 modifier to their attack (cumulative with the modifier if the attacker has to resort to running speed)
   3c. The character that is on the ground does not get to roll Reaction + Intuition against this attack, as he is considered out of control unless he succeeded the test in step 2

So, let's take an example. Jim gets pushed out of the back of a Toyota Gopher travelling at it's maximum speed of 4 (running).
1. Fortunately for Jim, the truck bed is only 1.5m off the ground, so he does not take any falling damage.
2. Jim rolls Gymanstics 4 + Reaction 4 (6) and gets 3 hits
   2b. Jim has failed to meet the threshold of Speed 4, and must now resist 8P using Body + Armor -6 AP
3. Since Jim exited the Gopher while it was doing Speed 4, Jim will be moving a total of 40/2=20 meters
   3a. Unfortunately for Jim, the driver of the Gopher had a friend following along in an Americar. This driver now rolls his Pilot Ground Craft 5 + Reaction 4 (5) with a -3 modifier, and since he is already moving at the Running Speed of his Americar he takes another -3 modifier for a total of -6. With only 2 dice he still manages to roll a 2 and a 6
   3b. Jim is in trouble, as he has no chance to avoid the car driving over him. A Speed of 3 is a Running Rate of 40m/CT, which gives a damage value of Body, in this case 11. Jim is in trouble, having to resist 11P with Body + Armor -6 AP, while the driver of the car has to resist (11/2 rounded up) = 6P as Jim's innards are splattered all over his grill. With an armor rating of 6, the only damage to the Americar is a dented fender.

Anyway, this is just how I would have handled it after a little deliberation. Feel free to use or modify as you see fit.

* I chose Reaction instead of Agility because in this case I feel it's more appropriate that the better reflexes you have the more you're likely to be able to use your Gymnastics skill.

[Reaver]

I would figure out the damage as if it was a crash, then halve it.