The luggage kept on the roof of the bus are tied with a rope so that it remains stable at one place and does not fall down because this luggage is not attached to the bus. When the bus is moving, the luggage on the bus may fall backwards from the roof of the bus, similarily when the bus stops suddenly, the luggage can fall forward. In such a condition the luggage is tied with a rope. This is due to inertia of rest luggage tends to keep moving when bus is moving and to remain stationary when it is stopped.