電車がガラガラ（すいている）って英語でなんて言うの？

"Wow, the train is empty today." When you add the "Wow" to this expression you are showing your surprise to the fact that the train is empty. You are used to seeing it very full but that day is not. "This train is usually packed but for some reason today is not." This is another way of saying the same thing. But this is a more formal way of saying it. In the U.S. this is a more popular way of saying such thing.

When we use the word "barely" we mean that there are few, a small amount or almost none of something. "There's barely anyone riding the train today."

The two sentences you see provided above are excellent ways to express to your listener that the train is normally full but today it was almost empty. In the first sentence you will see the word deserted. This means empty. This is a word that is common in our everyday conversation. It would make a great addition to your vocabulary.

If the train is normally busy/full then you could say 'the train is empty today' to expain that it is different you could also say 'there is hardly anyone on the train today' or 'the train is not as busy as normal'

If the train is usually very busy, with lots of people traveling on it, but today it is quiet, then any of the sentences above are correct. You are comparing today (a quiet day) with other days (busy). 'Usual' is a word that you use when talking about something that occurs frequently. For example: 'I usually brush my teeth after eating breakfast.' 'My son usually goes to bed at 8pm.' 'This train is usually busy, but not today.' 'This train is quieter than usual.' So you can use 'usual' to describe today's train as quiet, when usually it is busy/crowded.