Good point about Earth moving through space. It never occurred to me.
Like the other user stated, these are just movies. Don't overthink it.
—————-
\THX1701/

so, nobody is gonna touch on the whole "Earth moves through space, the Sol system is moving through the Milky Way" thing? um, locations in time & space would be SO far out of relativistic placement

We can't overthink these fantasy tales.
I'm an engineer, and if I allowed myself to sweat these details, I could never enjoy these types of movies.
For example (using the scene you mentioned) it would be impossible for 1985 train track to be in precisely the same place as it was in 1885. A fraction of an inch off and the DeLorean derails in a spectacular 88 plus mph fireball when it arrives back in the future.
Is very bad to steal Jobu's rum. Is very bad.

I think with the latter example you quoted they simply didn't have a choice. Even though it was a risk the only viable way to get the DL up to 88mph was to use the train.
Although it does make me think about the end of BTTF1. When Doc drops Marty off he goes straight to the future. How did he know Lyon Estates still existed in 2015? For all he knew it could have been knocked and apartments or a mall now stands where the street used to be. In fact how did Doc know 2015 was in the middle of WWIII? Guess you just gotta take the chance.
We have to show the world that not all of us are like him: Henning von Tresckow
.

Nicely done. It's Doc. He had the existing train schedules in 1985 memorized anyway!
You're makin' me beat up
GRASS!

Just think about the idea that Doc had it all planned/calculated out to send Marty back with just enough time to get out of the car safely before the train in 1985 would be coming through, not leaving Marty enough time to save it an insuring it gets destroyed like he wanted.
Channel Six News, they'll finger anything with a pulse!

It's indeed a risk they continuosly take, especially when travelling to the future. He can't know what's going to be there. Hell, he could arrive in the middle of a nuclear war for all he knows.
In fact, they almost crashed into a plane in the II movie.

It's the risk with any time machine that is moving at 88 mph as it moves backwards or forwards in time - you just don't know what object is or is not in that spacecould be a damned moose standing there.

Doc's crazy. He would have antipicated it because he almost crashed himself in part 2 when he first arrived in 2015.
He had Marty travel at 88mph in a 20mph zone on Main Street giving him no time to slam on the breaks crashing into the movie theater at the end of the block.
Tell you what…When I send my ex-wife her money…you can lick the stamps.

You're talking about a crazy scientist who , the first time he used the time machine after dropping Marty off at home, took off right down the street.

Doc's crazy. He would have antipicated it because he almost crashed himself in part 2 when he first arrived in 2015.
But it's a risk they have to take.
History is gonna change