I know nothing about camera stabilzers.  Would some sort of gyroscopic rig actually help, or are they just for video?

I've some experience with using a gimbal for video, but (at least with the one I have) it isn't a good idea for photos. The gimbal does NOT like you to touch the camera while it's trying to stabilize.  If you have a way to remotely release the shutter, then perhaps a gimbal will help. I don't think it gains much, though -- maybe a stop or two. It won't do anything for motion blur, of course.

You're very, very best bet is (as you know) the highest shutter speed you can use, even if you have to crank up the ISO (and, of course, open the aperture wide).

I've shot from moving cars in the past. Though I wasn't aiming for anything in particular, more just an experiment when I drove cross country. I don't do this anymore, as I've learned for the most part, I'm better off just pulling over and taking a photo outside of the car. Though just like your situation, I've gotten some nice landscape shots from the freeway where it is just not ideal to pull over to take photos.

But for your situation, I may do any of the following...

There are SLR camera mounts that you can mount your camera to either the outside or inside of your car.
https://www.bhphotovideo.com/c/buy/Camcorder-Mounts/ci/13931/N/4071351447
I've tried both inside and outside of my car. If you use it outside, you risk your camera falling of and damaging your car and other people's car. So I would add an extra cable tied to the camera to reduce risk. OR you could wind your window half way down and prop the lens out of the car while keeping most of the camera inside the car, this is where you mount the camera to the inside of the car passenger window. Or you could keep your car passenger window closed and mount your camera with a short lens inside, but you would probably need to use a lens skirt https://www.amazon.com/Lenskirt-Anti-Reflection-Portable-Flexible-Lens/dp/B005LAW7W8 to cover the camera lens and the window to block unwanted reflections.

Alternatively, you could just put your camera on a tripod on the front passenger seat and wedge it down with sandbags. You would still need to use a lens skirt to block out window reflections. Or just open your window. With the tripod be sure to wedge it down tightly. I had a situation when I wasn't even going that fast but the car in front of me forced me to do a sudden brake and my tripod with camera fell right into my car windshield and cracked it, causing a $1000 repair bill.

Alternatively you could just hand hold your camera, prefocus for the distance and just blindly press the shutter button, which is also something I've done in the past. This is the easiest method, but of all methods I've mentioned so far, probably the least successful at farming a photo properly.

You will also need a very fast ISO. Probably over a 1000ISO should do, but you will need to do your own testing. I would put your camera on P mode.

Back to the camera mount or tripod method, I would put a pocket wizard with cord attached to your camera. Then you can either trigger that pocket wizard directly, or have another pocket wizard in your hand to trigger that pocket wizard. Going by this method, it is best to pre-focus your camera.

Depending on how many cameras and pocket wizard you have or can borrow from a friend, you can also mount additional cameras on the back seat passenger window, then you get double the chances of getting that shot you want from one drive across the bridge.

OR have someone else drive the car, you hold the camera, put it on a fast ISO and shutter speed and your should be fine.

you'll definitely want to use the highest ISO your camera can handle / noise level you can reasonably fix.
the longer your focal length, the more pronounced your motion blur will be. and since you said your object is far, and likely wanting to be shooting long will get you way too much blur.

i don't know what a speed limit is there, but lets say its 60mph, = 3.802e+6 inches per hour, so 3,802,000 inches, / 60 minutes per hour = 63,366 / 60 seconds per minute = 1,056 inches per second, and then lets say you manage to get a 1/250s exposure, so divide one more time by 250, your camera's sensor is spanning 4.224 inches in a 1/250s exposure. which is huge.  you're still going to be very hard pressed to get a sharp image this way.

is it for stock? and what size do you need the image? may be better to shoot it as video and try to reconstruct it as a still;
http://www.cs.cornell.edu/~dph/papers/deblur.pdf

now thats a research paper and not any sort of software, so I don't know if there is any software out there that does this for you.. so its about as much of a longshot as trying to shoot that as a still i'd say.

I've never used my glidecam for still photos like this, but if i did, i'd probably want to trigger it wirelessly, so your camera should have the wifi connectivity / mobile app, and then you'd need to hold and steady it with two hands, and someone else to trigger it, and its still only a chance of it working. it may negate your up and down motion from something like a bumpy road but you're still traveling at interstate speeds which you can only cancel out by propelling your camera from the front of the car to the back of the car at the exact moment you shoot the photo� with an entirely unbroken window to shoot out of. haha. sounds like a photo for a superhero the more i think about it, which should make you happier when you actually get it!

good luck.

https://500px.com/photo/178998437/driving-fast-through-desert-in-vintage-hot-rod-car-by-joshua-resnick

I did this from the back of a minivan with the trunk door open and laying in the back with the camera hanging over the edge. Shot at 1/30th of a second. It is perfectly tack sharp somehow. Took a few thousand photos and about 10% were sharp.

It's an interstate highway with a minimal shoulder on the bridge - emergency stopping only.  Pulling over would actually be dangerous.

Tell the police it is an 'Emergency ' if you don't get the photo done right for iStock