乗る + に

The verb 乗る ('ride, board, get on') takes the vehicle with に, not を — 電車に乗る ('get on a train'), 自転車に乗る ('ride a bicycle'), 船に乗る ('board a ship'). Parallel to 会う + に — contact/entry verbs in Japanese often use に for what English treats as a direct object. The opposite direction uses を: 電車を降りる ('get off the train').