are able to climb stairs available to purchase. technical developments are continuing in this area. experiments have also been made with unusual variant wheels, like the omniwheel or the mecanum wheel. these allow for a broader spectrum of movement, but have made no mass-market penetration. the electric wheelchair shown on the right is fitted with mecanum wheels (sometimes known as ilon wheels) which give it complete freedom of movement. it can be driven forwards, backward, sideways, and diagonally, and also turned around on the spot or turned around while moving, all operated from a simple joystick. a beach wheelchair at a public beach in the netherlands a snow wheelchair at an outdoor park a leveraged freedom chair wheelchair user in kenya. the chair has been engineered to be low-cost and usable on the rough roads common in developing countries. wheelchair fitted with mecanum wheels, taken at an trade fair in the early 1980s other variants foot propulsion of a manual wheelchair by the occupant is possible for users who have limited hand movement capabilities or simply do not wish to use their hands for propulsion. foot propulsion also allows patients to exercise their legs to increase blood flow and limit further disability. users who do this commonly may elect to have a lower seat height and no footplate to better suit the wheelchair to their needs. wheelbase chairs are powered or manual wheelchairs with especially molded seating systems interfaced with them for users with a more complicated posture. a molded seating system involves taking a cast of a person's best achievable seated position and then either carving the shape from memory foam or forming a plastic mesh around it. this seat is then covered, framed, and attached to a wheelbase. a bariatric wheelchair is one designed to support larger weights; most standard chairs are designed to support no more than 250 lb (113 kg) on average. pediatric wheelchairs are another available subset of wheelchairs. these can address needs such as being able to play on the floor with other children, or cater for children in large hip-spica casts due to problems such as hip dysplasia. hemi wheelchairs have lower seats which are designed for easy foot propulsion. the decreased seat height also allows them to be used by children and shorter individuals. a knee scooter is a related device with some features of a wheelchair and some walking aids. unlike wheelchairs they are only suitable for below knee injuries to a single leg. the user rests the injured leg on the scooter, grasps the handlebars, and pushes with the uninjured leg. some walkers can be used as a wheelchair. these walkers have seat and foot plates, so an attendant can push while the patient is sitting on the walker. this is useful for a person who gets tired while walking with a walker, or has a limited walking range meaning the person can walk, but after a while, the person will collapse and fall to the ground. a commode wheelchair is a wheelchair made for the bathroom. a commode wheelchair has a hole in the seat so the user does not have to transfer into the toilet. sometimes the hole can be covered. sometimes there is a pan attached to the hole, so the user can urinate/defecate without having to wheel over the toilet. mobility and access wheelchair ramp and disabled parking space in california wheelchair ramp in the sejm, lower chamber of the polish parliament in warsaw a gate for wheelchairs in hiroshima a wheelchair-swing on a playground in new zealand the universal sign for disabled parking buildings adapting the built environment to make it more accessible to wheelchair users is one of the key campaigns of disability rights movements and local equality legislation such the americans with disabilities act of 1990 (ada). the social model of disability defines 'disability' as the discrimination experienced by people with impairments as a result of the failure of society to provide the adaptions needed for them to participate in society as equals. this includes both physical adaptions of the built environment and adaption of organizational and social structures and attitudes. a core principle of access is universal design - that all people regardless of disability are entitled to equal access to all parts of society like public transportation and buildings. a wheelchair user is less disabled in an environment without stairs. access starts outside of the building, with the provision of reduced height kerb-cuts where wheelchair users may need to cross roads, and the provision of adequate wheelchair parking, which must provide extra space in order to allow wheelchair users to transfer directly from seat to chair. some tension exists between access provisions for visually impaired pedestrians and wheelchair users and other mobility impaired pedestrians as textured paving, vital for visually impaired people to recognise the edge of features such as light-controlled crossings, is uncomfortable at best, and dangerous at worst, to those with mobility impairments. for access to public buildings, it is frequently necessary to adapt older buildings with features such as ramps or elevators in order to allow access by wheelchair users and other people with mobility impairments. other important adaptations can include powered doors, lowered fixtures such as sinks and water fountains, and accessible toilets with adequate space and grab bars to allow the disabled person to transfer out of their wheelchair onto the fixture. access needs for people with other disabilities, for instance visual impairments, may also be required, such as by provision of high visibility markings on the edges of steps and braille labelling. increasingly new construction for public use is required by local equality laws to have these features incorporated at the design stage. the same principles of access that apply to public buildings also apply to private homes and may be required as part of local building regulations. important adaptations include external access, providing sufficient space for a wheelchair user to move around the home, doorways that are wide enough for convenient use, access to upper floors, where they exist, which can be provided either by dedicated wheelchair lifts, or in some cases by using a stairlift to transfer between wheelchairs on different floors, and by providing accessible bathrooms with showers and/or bathtubs that are designed for accessibility. accessible bathrooms can permit the use of mobile shower chairs or transfer benches to facilitate bathing for people with disabilities. wet rooms are bathrooms where the shower floor and bathroom floor are one continuous waterproof surface. such floor designs allow a wheelchair user using a dedicated shower chair, or transferring onto a shower seat, to enter the shower without needing to overcome a barrier or lip. the construction of low floor trams and buses are increasingly required by law, whereas the use of inaccessible features such as paternoster lifts in public buildings without any alternative methods of wheelchair access is increasingly deprecated. modern architecture is increasingly required by law and recognised good practise to incorporate better accessibility at the design stage. in many countries, such as the uk, the owners of inaccessible buildings who have not provided permanent access measures are still required by local equality legislation to provide 'reasonable adjustments' to ensure that disabled people are able to access their services and are not excluded. these may range from keeping a portable ramp on hand to allow a wheelchair user to cross an inaccessible threshold, to providing personal service to access goods they are not otherwise able to reach. vehicles public transit vehicles are increasingly required to be accessible to people who use wheelchairs. in the uk, all single deck buses are required to be accessible to wheelchair users by 2017, all double-deck coaches by 2020. similar requirements exist for trains, with most trains already incorporating a number of wheelchair-spaces. the eu has required airline and airport operators to support the use of airports and airliners by wheelchair users and other 'persons with reduced mobility' since the introduction of eu directive ec1107/2006. in los angeles there is a program to remove a small amount of seating on some trains to make more room for bicycles and wheelchairs. new york city's entire bus system is wheelchair-accessible, and a multimillion-dollar renovation program is underway to provide elevator access to many of the city's 485 subway stations. in adelaide, australia, all public transport has provision for at least two wheelchairs per bus, tram or train. in addition, all trains have space available for bicycles. the washington, d.c. metro system features complete accessibility on all its subways and buses. in paris, france, the entire bus network, i.e. 60 lines, has been accessible to wheelchair users since 2010. in the united states, a wheelchair that has been designed and tested for use as a seat in motor vehicles is often referred to as a "wc19 wheelchair" or a "transit wheelchair". ansi-resna wc19 (officially, section 19 ansi/resna wc/vol. 1 wheelchairs for use in motor vehicles) is a voluntary standard for wheelchairs designed for use when traveling facing forward in a motor vehicle. iso 7176/19 is an international transit wheelchair standard that specifies similar design and performance requirements as ansi/resna wc19. there are special vans equipped for wheelchairs. these vans are large and have a ramp on a side door or the back door, so a wheelchair can get inside the vehicle while the user is still in it. some of the back seats will be removed and replaced with wheelchair security harnesses. sometimes wheelchair vans are equipped so the wheelchair user can drive the van without getting out of the wheelchair. a vehicle can be equipped with hand controls. hand controls are used when a person can't move their legs to push the pedals. the hand controls do the pushing of the pedals. some racecar drivers are paralyzed and use hand controls. public realm this footbridge includes a step-free ramp to assist wheelchair users. some elements of the outdoor public realm present barriers to wheelchair use, such as grade-separated areas where no ramps are provided. uk guidance recommends a minimum width of 1.5m for a wheelchair user and an ambulant pedestrian to move side by side; with maximum ramp gradients of 8% for manual wheelchair use (5% is preferred). distribution organizations several organizations exist that help to give and receive wheelchair equipment. organizations that accept wheelchair equipment donations typically attempt to identify recipients and match them with the donated equipment they have received. organizations that accept donations in the form of money for wheelchairs typically have the wheelchairs manufactured and distributed in large numbers, often in developing countries. organizations focusing on wheelchairs include direct relief, the free wheelchair mission, hope haven, personal energy transportation, the wheelchair foundation and wheelpower. in the united kingdom wheelchairs are supplied and maintained free of charge for disabled people whose need for such a chair is permanent. seating systems wheelchair seating systems are designed both to support the user in the sitting position and to redistribute pressure from areas of the body that are at risk of pressure ulcers. for someone in the sitting position, the parts of the body that are the most at risk for tissue breakdown include the ischial tuberosities, coccyx, sacrum and greater trochanters. wheelchair cushions are the prime method of delivering this protection and are nearly universally used. wheelchair cushions are also used to provide stability, comfort, aid posture and absorb shock. wheelchair cushions range from simple blocks of foam costing a few pounds or dollars, to specifically engineered multilayer designs with costs running into the hundreds of pounds/dollars/euros. prior to 1970, little was known about the effectiveness of wheelchair cushions and there was not a clinical method of evaluating wheelchair seat cushions. most recently, pressure imaging (or pressure mapping) is used to help determine each individual's pressure distribution to properly determine and fit a seating system. while almost all wheelchair users will use a wheelchair cushion, some users need more extensive postural support. this can be provided by adaptions to the back of the wheelchair, which can provide increased rigidity, head/neck rests and lateral support and in some cases by adaptions to the seat such as pommels and knee-blocks. harnesses may also be required. accessories there is a wide range of accessories for wheelchairs. there are cushions, cup holders, seatbelts, storage bags, lights, and more. a wheelchair user uses