Как правильно people travel by train, by plane, by boat, by car, by bike and on foot. или не нужно повторять предлог by people travel by train, plane, boat, car, bike and on foot.

People travel by train, by plane, by boat, by car, by bike and on foot.
People travel by train, plane, boat, car, bike and on foot.
Оба приемлемы.