A folding bicycle is a type of bicycle that incorporates hinges or joints in the frame and handlebar stem that permit it to be broken down into a more compact size. As well, most folders have wheels of 20 inch (51 cm) diameter or less. Folding bikes can be taken on public transport and into apartment buildings or workplaces where conventional bicycles are not allowed. This facilitates mixed-mode commuting, because a folding bike need not be parked in the street or train station.