The train will arrive at the station

[poli]

El tren va a llegar en o a la estación.

¿Cuál es correcto en or a?

[Rusty]

llegar a

[AngelicaDeAlquezar]

I agree with Rusty.

"Llegar en" is used to tell which means of transport was used to arrive at a place: "llegamos en autobús", "llegaron en coche", "va a llegar en bicicleta", etc.
That's why saying things in English like "we arrived to London" is a common mistake among Spanish speakers.

[poli]

That's what I thought too. I think there may me regional differences where enis preferred. I recently took a trip to Spain, and in the Madrid metro, before the train arrives a sign says el tren va a efectuar su entrada en la estación. The use of en seemed wrong which is why I put through the forum to see if you thought is sounded odd as well.

[AngelicaDeAlquezar]

I see, Poli.
"Entrar" may be used with "en" or "a" in this context, but "llegar" is a different verb.

We may say "el tren va a entrar en la estación" and "el tren va a entrar a la estación" with the same meaning. But with "llegar", we can only say "el tren va a llegar a la estación".