Как это сказать.

  • Как сказать "Я ехал в пустом вагоне"?

  • I was in a carriage with no passengers in it.

    I went /was going in a carriage , and there were no passengers in it.

    When I was going by train, I was alone/the only one in a carriage.

    Да, как угодно можно обыграть эту фразу. Главное---передать смысл.