Passengers are allowed to carry a limited number of smaller bags with them in the vehicle, these are known as hand luggage (more commonly referred to as carry-on in North America), and contain valuables and items needed during the journey. There is normally storage space provided for hand luggage, either under seating, or in overhead lockers. Trains often have luggage racks at the ends of the carriage near the doors, or above the seats if there are compartments. There are differing views between North America and Europe in relation to the rules concerning the amount of baggage carried on to aircraft. In North America there is considerable debate as to whether passengers carry too many bags on board and that their weight could be a risk to other passengers and flight safety. US airlines are beginning to introduce weight and size restrictions for carry-on baggage. Whereas in Europe, many airlines, especially low-cost airlines, impose what is commonly known as “the one-bag rule”. This is a restriction imposed to stop excessive weight on board and airlines claim that this policy allows them to speed the boarding of the aircraft. Airports in Europe have mounted a campaign with the European Commission in an attempt to overturn these hand luggage regulations.They claim that it is affecting their duty-free and other airport retail sales and is reducing their revenues.