|Version 4.0 July 9, 2001||
|Basics of Accessible Design||© Edward Steinfeld and Danise Levine, 2001|
|Contents||3. Site Design|
Summary of Design Criteria
Figure of site grading to provide access - SF State U. - Ed
Example from NYCHA showing good approach - done by Tamasha
Ramp with runnoff area - Ed's slides
from slides- Ed
Brick surfaces in Delft - Ed
Barcelona - Ed
Guide strips - Ed
Van unloading - from web site advertising van lifts - Danise
Good signage from U. - Danise
Swimming pool in Atlanta - Visitability slides - Ed
One of the most important aspects of barrier-free design is providing the means by which people with disabilities can get to a site and use facilities in a building. By considering accessibility at all stages of site design, architects can often avoid serious difficulties in meeting accessibility codes. At the same time, they will discover that the resulting outdoor spaces will generally be more convenient and safer for all users.
General Planning Concepts
Most accessibility codes require only one entrance of a building to be accessible. Logically, this accessible entrance should be the one closest to major site access points - bus stops, parking facilities, public sidewalk or entrances of adjacent buildings with related use. If this entrance is also the principal entrance of a building, it will benefit users in general because it will be direct and convenient. But what if there is more than one major site access point and they are far apart? Given such conditions, multiple-entrance or entry court schemes could be used as basic design concepts.
A building often can serve as a circulation link between two major generators of pedestrian traffic. In extreme climates, designing a building in such a location to include a public access way provides beneficial shelter during the worst season of the year. But a building with only one accessible entrance eliminates its use in this way. Moreover, since every building is closed at times, it is important that the path through the building not be the only accessible path from one end of the site to the other.
It is a fallacy that steep sites are always more difficult to make accessible. Sometimes, steep sites provide opportunities for direct access to intermediate floors as well as the ground floor. In making a steep site accessible, a key principle is to orient the circulation system with the contours rather than against them. This will minimize stairways and ramps and help to reduce the grade of the main pathways.
The minimum circulation width necessary for passage is 36 in.; this width is based upon the spread of crutch tips and the space necessary to wheel a wheelchair, allowing for some deviations from a perfectly straight push. The actual width of any walk segment, however, must be based upon the directions of traffic flow, the volume of traffic, the length of the segment and surrounding site conditions. In general, where traffic is in two directions, providing places large enough for two wheelchairs to pass each other (a 60- by 60-inch space) at reasonable intervals is a satisfactory way to ensure that passage will not be restricted. This space can include the walk width itself; for example, a 48-inch-wide path would only have to be widened 12 in. at intervals to provide such a place. Also, “T” intersections of pathways can be used for passing places.
Many individuals - both those who walk and those who use wheelchairs - have difficulty negotiating inclines above a slope of 1:20. The difficulty of any given incline is relative to both its slope and length. Research has found that many wheelchair users cannot negotiate the widely used slope of 1:12 for a distance of more than 20 feet, but most of those people could manage a 1:16 slope for 30 feet. In another study, wheelchair users rated a slope of 1:8 to be relatively easy for a distance of two feet, but, this slope should not be used in new construction. . Ramps steeper than 1:8 are hazardous due to the danger of overturning and collision of footrests at the bottom of the ramp. Ramps should have runoff space at both top and bottom and railings at both sides unless they are very short and have protected sides, e.g. flares, walls or landscape elements that prevent people from walking accross the ramp.
On building sites and public walks, the most frequent need for ramps is at street curbs. People using curb ramps must be protected from automobile traffic. Where there are marked street crossings, curb ramps should always be placed within the marked boundary. Curb ramps should only be placed at the apex of a corner where the radius of curvature of the curb is large enough so that the run-off space at the bottom of the ramp is not within the traffic lanes. Short ramps for mounting curbs do not need railings. Curb ramps should have flared sides that blend into the surrounding walkway or road. These flares should not be steeper than 1:10 or they will create a tripping hazard for ambulatory individuals when walking across the ramp. Flares are not needed where landscape elements prevent people from walking accross the curb ramp.
Wheelchairs cannot be used effectively on surfaces that are soft, internally unstable, poorly maintained or depart too greatly from level. Wheelchairs and walking aids are extremely difficult and sometimes dangerous to use on irregular surfaces (e.g., cobblestones) or other surfaces that have small components with unfilled joints. Gratings and ridges on walking surfaces should be eliminated to ensure that those people with poor sight or shuffling gaits will not slip or trip. Drainage grates can be placed to the side of pedestrian areas. Excessive cross slope or crowning can make it impossible to propel a wheelchair in a straight line and can also upset the balance of walking aid users and others with impaired gaits. Where pathways end at doors and gates, there must be enough maneuvering space to approach, open and pass through them. This space has to be relatively level or wheelchair users might roll away as they try to pull the door or gate open.
People who have severe visual impairments are trained to use curbs to identify the boundaries between paths and streets. Although complete removal of curbs helps to provide access for wheelchair users and others who have difficulty walking, it eliminates a major safety feature for visually impaired individuals. Urban design projects in many cities have eliminated curbs at intersections entirely. Changes of material are used to separate the vehicular from pedestrian areas. Such intersections can be very dangerous for people with visual impairments who use the long cane as a mobility aid. They may not find the edge of the vehicular area and can wander out into the street unaware of the danger. Moreover, visually impaired travelers who use the long cane need to “square off” at the street edge in order to cross in the right direction. They use the curb to do this. Therefore, it is not advisable to remove the entire curb unless some fail safe method is used to mark the street edge. Curb ramps should be located to the side of the most direct line of pedestrian traffic. Cane travelers can then find the curb easily.
Tactile warning surface treatments have been recommended as a means to mark the boundary of hazardous pedestrian areas. They are materials that provide a distinctive audible, tactile and rebound “signature” when tapped by a cane or walked upon. Such surfaces can also be used to mark unexpected and extreme hazards such as the top of stairs located in the middle of a walk or plaza, the edge of public transit loading platforms, and the edge of reflecting pools not otherwise protected. There is considerable debate about the usefulness of these surfaces. Some research has demonstrated limited effectiveness while other research raises serious questions about their usefulness (see Communications in Buildings). Guide strips built into the walkway are another means to help visually impaired people find their way. These strips could also be impediments to safe walking and easy wheeling if not designed carefully.
Most vans are equipped with mechanical platform lifts to provide access to the vehicle. A side lift with access perpendicular to the van requires about 7 feet of space for wheelchair maneuvering, and the lift itself. Since cars are about 1.5 feet narrower than 8 ft. wide parking spaces, with an 8 ft. space there should be about one ft. of available space on either side of the access aisle to provide additional space. However, often the van and the car on the opposite side of the access aisle are not pulled over to the extreme side of their respective spaces. This situation may make it impossible to gain access to such a lift. Thus, regulations like the ADAAGrequire a specified minimum number of “van accessible” spaces with 8 ft. wide access aisles. The UFAS provides criteria for van accessible spaces but does not specifically require any. A new type of lift pivots 90° as it extends out of the van. These only require about 30 in. of transfer space since the lift is mounted in a direction parallel to the vehicle. However, this type of lift is still relatively rare.
The need for accessible spaces varies considerably with the number of spaces in the lot and the type of buildings served by lots. Experience has demonstrated that the proportion of spaces allocated to disabled drivers can be reduced as the number of available spaces increases. But, in lots serving health care facilities, the proportion of accessible spaces should be much higher than for other facilities. At least one van-accessible space should be provided and more in large lots. The ADAAG and state codes have formula that establish minima in proportion to the total number of accessible spaces as a whole. No empirical research has been completed on this subject. Such research would help to identify more precise estimates on the demand for accessible spaces.
In lots where spaces are not assigned for use to individuals, accessible parking spaces must be reserved for drivers with disabilities and appropriately marked by a sign. In lots where spaces are assigned, the number of accessible spaces provided would be based on the needs of individuals. Even accessible spaces in assigned lots should have signs. The sign should be high enough so that police or traffic safety officials can see it easily. This will promote effective enforcement of the rules.
The accessible spaces should be along the shortest accessible route to the building entrance they serve. Where there are several lots serving an entrance, it is better to locate all accessible spaces in the closest lot rather than assigning an equal number to all lots. Vans can be much higher than the beams or ceilings of parking garages. Where such structures do not allow at least 9 ft. of headroom, additional spaces in locations that have such a clearance should be provided. Sometimes, a parking lot serves more than one building. In that case, where should the accessible parking be located? If it can be located equidistant from the accessible entrances to buildings served by the lot, that is usually the best location.
Automobile loading zones serving buildings should have a clear transfer space parallel to where the vehicle parks, wide enough for a person to transfer to and from a vehicle. A curb ramp is necessary somewhere in the loading zone for people who cannot manage a transfer directly to and from a curb, or for reaching buses that may not be able to approach the curb.
Site Furniture and Amenities
Many objects mounted on pylons, posts and walls overhang circulation paths. Blind and partially sighted people can easily injure themselves by bumping into those objects which are not detectable by canes. Overhangs with their leading edges no greater than 27 in. high can be detected. If the edges are higher than that, the object should be protected by guide walls or moved out of the circulation paths. Objects mounted on posts or pylons can be detected with a cane before collision even if their leading edges are higher than 27 in., as long as the overhang from the post or pylon is minimal. Regulations allow a 12 in. overhang, but, some visually impaired people feel that any overhang outside cane range should be eliminated.
Where tables, seating and other site amenities are provided, enough should be located on accessible routes and designed for use by people with disabilities so that they can participate fully in all site activities. This does not mean that all amenities must be located along accessible routes - only those that are necessary to make the full range of site experiences available.
One of the most important types of site amenities is the playground. Although it is not necessary that every piece of equipment be fully accessible, enough of it should be so that children with disabilities can maintain interest and obtain challenges using the playground. There are many examples of accessible play equipment. a stable safe surface is another important feature of accessible play areas. Recently, firm plastic materials have been developed for use in playgrounds that provide both a stable surface and reduce injuries from falls.
Another important amenity type is the swimming pool. Swimming is an activity that many people with disabilities use for fitness and therapy. Pools can be made accessible either by ramps, stairs or by hydraulic lifts. The ramp is preferable since it provides the most convenient access to the pool. A non ambulant person can lower themselves step by step into the pool. The lift usually requires a trained operator. Using one can be a frightening experience, especially for the first time.