<P> Door brakes exist because the doors on the first vehicles were heavy, so they had to be pushed hard to make them close . Soon after, automotive manufacturers managed to construct lighter doors, but users were used to closing doors with force so doors quickly became damaged . Door brakes were then introduced to slow down the door just before the door closed to prevent damage; these soon became standard . </P> <P> Hatchback and estate or station wagon bodies are sold as' three - door' or' five - door' models . In these cases, the rear hatch is classified as a door; this is because it enters the passenger compartment . With other vehicles such as saloons or sedans and coupés, the boot / trunk lid is not counted as a door by definition because it is for a separate storage compartment - these cars are sold as' two - door' or' four - door' . This system is mainly used in Europe, and is less common in North America . In Europe, the American - style labelling is occasionally used . </P> <P> Usually in North America, cars are only sold as "two - door" or "four - door" models . This American - style labelling only includes the passengers' and driver's doors, and not hatches on hatchbacks and station wagons . This has led to many not understanding that hatches are counted as doors in Europe, whilst the lids to sealed trunks aren't . </P> <P> Some cyclists refer to colliding with an open car door as "being door checked". This usually happens when the cyclist is riding alongside a row of parallel - parked cars, and a driver suddenly opens his or her door immediately in front of the cyclist without first looking to see if it is safe to do so . </P>

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