This is the 3912th most frequent Korean word.
열차에
"열차에" means "on the train" or "to the train" in English.
Here, "열차에" refers to the train as the vehicle into which people are boarding.
열차에 사람들이 많이 타고 있습니다.
Many people are boarding the train.
In this sentence, "열차에" indicates the location within the train where seating is being discussed.
내일 아침에는 열차에 앉을 자리 있을까요?
Will there be seats available on the train tomorrow morning?
"열차에" here pertains to the subject matter or topic concerning trains.