I honestly would like to see them instead of having to use Fast Travel, which I don't use anyway, but I'm not sure if they would work?

No. The roads and terrain are not conducive to vehicle travel. Maybe, I stress MAYBE a dirt bike would work, or a horse type creature.

I would like a vehicle of some kind. I loved the motorcycle mod I used in Fallout 3. It was a must-have in all my games. I think something similar would be great.

Not without a significant update to the game engine or larger map size.

They tried carrages in Skyrim (which runs on a prior version of the engine), and they ended up turning it into a fast-travel lite thing, due to the fact that the slightest dip or rock would wreak havoc on the carraige. And that's in a game where most of the roads AREN'T crater-filled, rubble-strewn messes.

Also, vehicles are much faster than walking or running, which means they'd need to increase the map size significantly. Otherwise, there would be complaints that your motorcycle moves too slow, or the world is incredibly small.

Finally, if the speed if a vehicle isn't capped, you could easily hit a loading screen while outside every three seconds, as you exceed the immediate area that the game loaded. It would then need to stop you and load the next section of cells.

The Power Armor is the Vehicle ^^

You mean, https://www.youtube.com/watch?v=iKxmjOTaEO0

I kid with that video. However, I cannot play FO3 without the Motorcycle Fast Travel mod. It...

... just works.

There should be cars or motorcycles in the game logically (think about it - they are able to salvage and repair power armor, but not cars?), but I don't think these games should have them. You could maybe make a case for a motorcycle, but definitely nothing bigger than that.

At that point the setting just becomes Mad Max in Boston. Fallout is about creeping through an eerie wasteland where you could be set upon at any time by... something. It's not about whipping through the landscape at 90mph - which would also make the world feel a lot smaller.

Being able to fast travel to discovered locations is good enough for me. The movement in this game never feels particularly slow, even when you're out in the open.

land vehicles not really but air vehicles like the vertibird could work