Sidewalk/street transitions, curb ramps, transition ramps, and landings in the public right-of-way shall comply with Section X02.4.
Discussion: In keeping with a "kit of parts" approach, the committee recommends new names for the parts of the system that transition from roadway to public sidewalk level. The new terms identify function rather than geometric orientation of the ramp. Curb ramps cut though the face of the curb, and may or may not be perpendicular to the curb line. Transition ramps transition between upper and lower landings within the public sidewalk. Some transition ramps are used to allow the public sidewalk to dip down at driveways, at intermediate locations in the block.
By using this flexible kit of parts, designers can create access between public sidewalk and roadway level with a combination of approaches.
X02.4.1.1 Where required. A curb ramp or flush landing shall be provided wherever the pedestrian access route crosses a sidewalk/street transition, including intersections, mid-block crosswalks, medians and islands traversed by crosswalks, alleys, accessible parking aisles, passenger loading zones, and locations where the public sidewalk ends and pedestrian travel continues in the roadway.
EXCEPTION: A curb ramp or flush landing is not required where the pedestrian access route crosses a driveway and the elevation of the pedestrian access route is maintained.
X02.4.1.2 Corners. At any intersection in the public right-of-way that has at least one corner served by a public sidewalk or a pedestrian access route, all corners of the intersection served by a crosswalk shall have curb ramps or flush landings.
Curb Ramp: isometric view of a curb ramp as currently defined. The illustration is based on the old "perpendicular" style ramp.
Transition Ramp: isometric view of a transition ramp as currently defined. The illustration is based on the old "parallel" style ramp.
Shared ramp shows a single ramp used for two crossing directions.
The top one shows an assembly that might be used at a mid-block crosswalk, and combines transition ramps leading to a landing and from there access to a single curb ramp at right angles to the transition ramps. The bottom one shows a corner where the sidewalk is dropped by transition ramps to a lowered elevation, from which two separated curb ramps provide access to the street.
The top diagram shows a built-up curb ramp entirely beyond the curb line with a note that this arrangement is not to be used in traffic lanes. The lower diagram shows a curb ramp that projects partially beyond the curb line.
Shared Transition: a combined approach with two transition ramps on a curved corner approaching a single landing area that is blended with the vehicular way.
Discussion: The committee concurred that curb ramps or flush landings were required at every corner, to eliminate the possibility of a pedestrian entering a road, traveling across the road, then finding no refuge at the other end of the crosswalk. The intent is that there be, at minimum, a landing at each corner, either at roadway level (flush landing) or sidewalk level (behind a curb ramp). If there are two curb ramps or flush landings placed on an otherwise undeveloped corner, they should be connected to each other and to any pedestrian call button, so that a pedestrian can have a refuge while deciding whether to continue on the shoulder or turn around.
X02.4.1.3 Number. Where curb ramps or flush landings are required, there shall be a separate curb ramp or flush landing serving each direction of travel, whenever technically feasible.
Discussion: The committee strongly discourages the use of shared curb ramps, formerly called diagonal curb ramps, or shared flush landings , formerly called single parallel curb ramps, unless there is no alternative. No specific exceptions were agreed upon. The committee clearly did not want jurisdictions to use shared curb ramps or flush landings as a matter of course, simply because they are cheaper to install. Some of the reasons against shared curb ramps and shared flush landings are:
The committee recognized that intersection geometry can preclude the placement of separate curb ramps or flush landings for each crosswalk. The combination of such variables as curb radius, sidewalk width, and furnishing zone width, create situations where shared curb ramps or flush landings are the only possible alternative. Some examples are:
Where the above conditions exist, designers are encouraged to try to reduce the curb radius or take other measures to eliminate the need for shared curb ramps or flush landings.
There are some situations in which a shared curb ramp or flush landing can be made extra wide, thereby enabling it to serve both directions of travel without deflecting the pedestrian into the parallel vehicular pathway. The problems of longer crossing distances and unexpected pedestrian departure points may still exist. Such situations include:
X02.4.1.4 Landings. There shall be a landing at the top of each curb ramp. There shall be a landing at the top and at the bottom of each transition ramp. At each sidewalk/street transition where a curb ramp is not needed (for example , where the sidewalk elevation is dropped to roadway elevation), there shall be a flush landing provided at the roadway level, in the pedestrian access route. Landings may overlap with adjacent landings or a single landing may serve multiple ramps.
EXCEPTION: Where the public sidewalk or pedestrian access route elevation is lowered to cross an unsignalized driveway, landings are not required. However, successive curb ramps or transition ramps shall be separated by at least 60 inches (1525mm) in the direction of travel on the pedestrian access route.
Discussion: Landings are needed in public sidewalks before pedestrians cross into the roadway, even if the public sidewalk and the roadway are at the same elevation. Landings are unobstructed level areas used for turning (including U-turns), accessing pedestrian signal call buttons, resting, passing, and waiting for a safe crossing time.
There was considerable debate about the recommendation to require landings at the top of transition ramps. The vote on this recommendation was very close. The rationale for requiring a landing is to provide a place for a pedestrian to rest after climbing the ramp, before attempting a steep sidewalk grade. However, in steep terrain such a landing may have the effect of making the sidewalk even steeper. Where the roadway grade is more than about five percent and the sidewalk is immediately adjacent to the curb, placing a landing at the top of transition ramps may be technically infeasible.
The committee found that an exception to the landings requirement was necessary for some types of driveways that cross public sidewalks. The exception is limited to driveways that lower the sidewalk elevation across the driveway opening. In many locations, it would be difficult to make the sidewalk relatively flat at each driveway. Since the pedestrian is traveling on a public sidewalk, and a driveway is a crossing of a public sidewalk, the pedestrian retains the right-of-way over the vehicle. The pedestrian is not required to stop and wait for vehicles, therefore the landing is not necessary. However, at signalized driveway crossings, where traffic volumes are greater and pedestrians are compelled to wait to cross, a landing is required for pedestrian safety.
Curb ramps, transition ramps, flush landings and maneuvering spaces shall be placed in accordance with this section.
X02.4.2.1 Street interface. The bottom of the curb ramp run, exclusive of flares, shall be wholly contained within the markings of the crosswalk or access aisle that the curb ramp serves and may not protrude beyond the curb line into the path of vehicles. Beyond the curb line, there shall be a minimum maneuvering space of 48 inches by 48 inches (1220 by 1220mm). The maneuvering space shall be wholly contained within the crosswalk and shall be wholly outside the parallel vehicular travel path. Where flush landings are provided, they shall be placed so that the expected path of a pedestrian entering the crosswalk or access aisle is wholly contained within the crosswalk or access aisle and wholly outside the parallel vehicular travel path. At passenger loading zones, the curb ramp or flush landing shall be placed in accordance with section Section X02.6.3.
EXCEPTION: A curb ramp may project into an accessible parking aisle if the ramp does not intrude into maneuvering and unloading areas.
Discussion: Flush landings are sometimes larger than the crosswalk, especially if a single flush landing is shared between two crossing directions. The landing and crosswalk must be oriented to each other such that a pedestrian can wait at the landing, oriented in the direction of the crosswalk, and enter the crosswalk when safe to do so.
When a curb ramp is placed at a slight skew to the crosswalk, the same problems of turning and orienting occur as discussed above in the proposed rule relating to shared curb ramps. The crosswalk must be wide enough to allow for maneuvering at the curb ramp departure without entering parallel vehicular traffic. The maneuvering space of 48 inches by 48 inches is not technically a landing, because the slope in the roadway may exceed 1:48, but it serves the purpose of providing space for the pedestrian using a wheelchair or other mobility aid to align properly with the curb ramp.
Curb ramps that project into the vehicular travel path are prohibited because they are a hazard to pedestrian and vehicular travel. Projected curb ramps may result in ponding of storm water and the accumulation of ice.
X02.4.2.2 Sidewalk interface. Curb ramps shall be wholly contained within the public sidewalk.
X02.4.3 Directionality. RESERVED.
Advisory: The curb ramp should generally align with the expected path of travel to provide directionality, provided that the cross slope of the ramp does not exceed 1:48.
Illustration of a curb ramp that exhibits directionality to the crosswalk and the sidewalk, while complying with warping and cross slope requirements.
Discussion: The committee strongly supported both the idea of aligning curb ramps with the direction of the crosswalk (directionality) and minimizing the problems for wheelchairs that are caused by skewed approaches, warping at the foot of the curb ramp, or cross slope in the curb ramp. Recognizing that the ideal cannot always be achieved, the committee supported directionality, but not at the expense of excessive cross slope and warping.
Blind and visually impaired pedestrians use several different cues to align themselves with the crosswalks at intersections. One cue can be to determine the alignment of the curb ramp by its falling grade to the roadway. When the curb ramp is aligned with both the sidewalk and the crosswalk, visually impaired pedestrians have a straight line of travel. The straight line of travel usually dictates that the ramp cross the corner radius at a skew.
However, ramps that cross the curb at a skew may cause a wheelchair to become unbalanced. The cross-slope of the ramp, the gutter grade, the street crown grade, and the skew angle of the ramp all combine to cause one or two of the wheels of a wheelchair to lift from the ground surface. With one or two of the wheels in the air, the chair user experiences some loss of control until the wheelchair again finds four points of support. The instability problem can be minimized by having the wheelchair cross the curb at a right angle. This requires a radial alignment of the curb ramp.
The committee found that the needs of both visually impaired and wheelchair travelers could be generally be satisfied in only two situations: very flat intersections or corners with a very small radius.
Intersections at or below two percent grade in all directions would allow the construction of ramps that entered the street with little or no cross-slope. The instability problem for wheelchair users would be minimized since there would be no warp in the curb ramp and there would be no counterslope problems between the ramp and the street grade. The ramps could be aligned with the direction of travel minimizing changes of direction for the visually impaired.
Corners with very small corner return radii have straight sections of curb within the corner area that can accommodate curb ramps which are both directional and perpendicular to the curb line. However, the committee recognizes that the use of small corner return radii can affect vehicle turning movements and that this solution will not be appropriate in all cases.
Research need: The committee identified a need for additional information and research on the use of tactile cues for directionality that do not rely on the curb ramp direction. A number of possible strategies to provide directional and alignment information to individuals who are blind or visually impaired were considered by the committee. These included tactile guidestrips, directional bar tiles, alignment of the detectable warning, and raised crosswalk lines. Tactile guide strips have been used in some locations in San Diego and San Francisco. These have been constructed of metal, concrete, or plastic and embedded in the street in the center of the crosswalk area. Directional bar tiles have lozenge shaped raised sections (similar in height to the truncated domes of detectable warnings) intended to be oriented in the direction of travel. These are used in England, Sweden and Japan. Raised crosswalk lines were also suggested, with photos presented of an example using concrete tiles to outline the crosswalk as well as a discussion of the use of thermoplastic markings. However, concerns regarding detectability and maintenance were raised, as well as concerns about the impact of such surfaces on wheelchair users.
The clear width of a curb ramp run shall be not less than 48 inches (1220mm), excluding flares. The clear width of a transition ramp shall not be less than the width of the pedestrian access route.
Discussion: Recognizing that the curb ramp can be a bottleneck to pedestrian flow, the minimum clear width of four feet matches the minimum 48-inch width of the pedestrian access route in several areas where exceptions to the 60-inch width are permitted. Wheelchair bases have gotten wider in recent years and three-wheeled scooter use has become more prevalent. In addition, the wider curb ramp widths allow for some wheelchair maneuvering on the curb ramp to adjust for approaching curb ramp bottoms that are skewed. Where possible, a wider ramp with a 60-inch width is encouraged to allow for two wheelchairs to pass, particularly in areas where higher wheelchair usage is prevalent. In the past, wider curb ramps raised some concern because the width of depressed curb might confuse a blind pedestrian. With the inclusion of detectable warning surfaces (see Section X02.5.7) at the foot of curb ramps, this concern is no longer significant.
Transition ramps must be the width of the entire pedestrian access route to accommodate all pedestrian traffic wishing to enter the street. Since they do not have flared sides, transition ramps could introduce a tripping hazard or be undetected by pedestrians with low vision if they are not the full width of the public sidewalk. Unlike curb ramps, which can be used selectively by those pedestrians that prefer them, a transition ramp is generally used by all pedestrians. Therefore, it should be wide enough to allow for pedestrians that travel with a service animal or a pedestrian guide, and still allow for pedestrian traffic in the opposite direction to pass.
X02.4.5 Landing size.
Landings, including flush landings, shall have a minimum clear dimension of a 60-inch by 60-inch (1525 by 1525mm) square or 60-inch diameter circle. Landings may overlap with adjacent landings or a single landing may serve multiple curb ramps or transition ramps. Landings may overlap with the clear ground or floor space required at push buttons.
Discussion: Landings provide the clear level space at the top of the curb ramp, or flush with the street behind the sidewalk/street interface, that allow space for the user to maneuver and wait. Minimum landing dimensions are derived from the need to provide a five-foot diameter turning circle. Landings need to be positioned at locations that provide the user with directional choices or where the user must wait for a suitable time to cross the street. As with the width of curb ramps, landing dimensions must provide for turning and maneuvering needs of three-wheel scooters, which have longer turning radii than wheelchairs. Landings are critical to maneuvering at curb ramps, and they allow for passing between two wheelchairs or scooters. Landings may also provide access to pedestrian signal call buttons, and must be large enough so that the pedestrian can approach the button, operate it, leave the button, and orient to the crosswalk while awaiting the signal. All of this must occur on an unobstructed level surface.
Utility supports and other obstructions may not be located within the minimum clear landing dimension or the clear space approach to the pedestrian signal call button.
Flush landings provide a clear level space on the sidewalk, prior to entering the street, for the user to maneuver or wait.
X02.4.6 Running grade.
The maximum running grade of any portion of any curb ramp or transition ramp shall be 1:12 as measured from a level plane.
EXCEPTION: Curb ramps and transition ramps are not required to be longer than 15 feet.
Discussion: On streets where grades are steep and it is difficult or impossible for the transition ramp or curb ramp maximum slope of 1:12 to intersect the street grade, a steeper grade may be used to limit the run to 15 feet in length. It should be noted that the limit proposed in the Interim Final Rule was 96 inches, which applied only to parallel curb ramps (transition ramps in this document). The 15 foot maximum proposed here is an attempt to find a reasonable compromise between what is accessible and what is technically feasible in the case of steep grades.
The committee discussed the fact that there are situations where a curb ramp or transition ramp would need to be greater than 15 feet in order to achieve the 1:12 grade and it would not be difficult to do so because the grade of the terrain or adjoining roadway is not steep. One example is where the sidewalk elevation is 15 inches or more above the street. Where the construction of a curb ramp or transition ramp longer than 15 feet is possible, the 15-foot limitation should not be invoked to create unnecessarily inaccessible sidewalks. The committee agreed that the limitation should apply only to curb ramps or transition ramps adjacent to roadways or terrain having a grade greater than a certain percentage, but, due to insufficient time for consideration, did not determine what that percentage should be.
X02.4.7 Cross slope and warp.
The maximum cross slope of curb ramps and transition ramps, measured perpendicular to the direction of travel, is 1:48. The maximum cross slope at landings is 1:48 in any direction. Surfaces shall generally lie in continuous planes with a minimum of surface warping.
EXCEPTION: Where the base of the curb ramp or the edge of the flush landing must join a street with a running grade greater than 1:48, the base of the curb ramp or the edge of the flush landing may be warped to meet the street running grade.
Discussion: Generally, with the limitation of 1:48 on crosswalk cross slope, warping will not be required in new construction. The committee found that the planar surfaces, those with little to no warping, would ensure that all wheels of a wheelchair would be in contact with the travel surface. For the wheelchair user, the planar surface yields the highest possible degree of stability and mobility. The committee also recognized that warping of ramp surfaces will be a factor in both new construction and certainly in alterations.
Research need: Research is needed to indicate what maximum warp condition can be tolerated without causing a tipping hazard for pedestrians using wheelchairs, scooters, walkers or other mobility aids. Research is also recommended to develop design alternatives to minimize adverse effects on wheelchair travel from surfaces that are warped.
X02.4.8 Counter slopes.
The grade break between the counter slopes of gutter and/or road surfaces within 24 inches of the curb ramp and the running grade of the curb ramp shall not exceed the algebraic difference of 11 percent. If two or more plane changes are present, they shall be separated by 24 inches (455mm).
Figure X02.4 H Counter Slope Conditions
Sectional view of wheelchair at a counter slope condition with grades indicating the algebraic differences and limitations. Second view showing double grade break.
Discussion: Gutter counter slope is the angle point or grade change where the down slope of the curb ramp meets the up cross slope of the gutter. Steep counter slopes will cause some wheelchairs to catch on back rollers and lose drive wheel traction. For others, the steep counter slope will catch footrests. Many road standards set a standard gutter cross slope at 5 percent. The committee voted to set the maximum grade change at 11 percent to avoid causing problems for some wheelchair users. The committee did consider other alternatives, including maintaining the current 13.33 percent, however due to insufficient data, the committee felt that the flatter 11 percent standard would be safer. If the curb ramp is set at 1:12 (8.33 percent) and both were built to maximum standard, then the resulting algebraic difference in grade would be 13.33 percent. Consequently, gutter cross slope may need to be lessened at intersections or other locations where curb ramps are placed. Also, this standard could be met by lessening the grade of the curb ramp.
Some members felt that the existing 13.33 percent limit would be adequate if constructed properly and that more enforcement, rather than stricter requirements, was necessary. Other members suggested that more research on riding surface angles and clearances under the wheelchair footrest were necessary. Some members felt that wheelchair designers and manufacturers had some obligation to produce wheelchairs that would accommodate the users needs and have the ability to safely operate in a street environment. Some recent innovations in the caster wheel design do show some promise in making wheelchairs better at negotiating grade changes.
X02.4.9 Edge conditions.
The edges of the public sidewalk shall comply with the requirements of this section.
X02.4.9.1 Flares. Curb ramps located where pedestrians may walk across the curb ramp shall have flared sides. The length of the flares shall be at least ten times the curb height, measured along the curb line. Curb ramps with returned curbs shall be permitted where pedestrians would not normally walk across the curb ramp. Where a sidewalk splits, and only part goes down a transitional ramp, the split edge shall be protected with landscaping, railings, or other fixed barriers. Curbs may be used to separate landscaping or other features from landings but should not be placed so as to block permitted travel to an unimproved surface.
Discussion: Notice that the slope of the flare is 1:10 relative to the plane of the curb, not to a level plane. In the public right-of-way, flares are not considered a part of the pedestrian access route. The 1:10 slope relative to the plane of the sidewalk is sufficient to avoid a tripping hazard, and allows the flares to be built symmetrically, even on sloping terrain. The majority of curb ramps are already built this way.
Since there is a mandatory 60-inch top landing at each curb ramp, there is no need for the ADAAG provision for 1:12 slopes on flares where the width of the walking surface at the top of the curb ramp run is less than 48 inches.
Isometric view of curb ramp with sloped sides describing the required length of the slope and measurement method (10x the curb height, measured at the face of the curb).
X02.4.9.2 Curb returns. Curb ramps with returned curbs shall be permitted where pedestrians would not normally walk across the curb ramp.
Discussion: Flares are not necessary where pedestrians would not be expected to cross the edges of curb ramps, such as in medians or where there is landscaping or a fixed obstruction blocking such circulation.
X02.4.9.3 Diverging grades. Where a public sidewalk diverges, with only part becoming a transition ramp, the area where the surface grades diverge shall be protected with clearly defined surfaces such as landscaping, railings, or other fixed barriers.
X02.4.9.4 Curb placement. Curbs may be used to separate landscaping or other features from landings but should not be placed so as to block permitted travel to an unimproved surface.
Discussion: At some corners, there is an improved sidewalk entering from one direction, and an unimproved pedestrian path behind the curb entering from the other direction. The landings should not be built with curbing around the back that would be a barrier to travel on the unimproved surface.
The surface of curb ramps and landings shall be stable, firm and slip resistant and shall lie generally in a continuous plane with a minimum of surface warping. Gratings, access covers and similar surfaces shall not be located on curb ramps, transition ramps, landings, or gutter pans at the sidewalk/street transition.
Discussion: The surface requirements for curb ramps and landings in the public right-of-way are consistent with the surface requirements in proposed ADAAG.
X02.4.11 Vertical grade breaks and lips.
There shall be no vertical change in level on a curb ramp or transition ramp, on a flare, in a landing, in the gutter pan at a sidewalk/street transition, or between curb ramps, flares, landings, gutter pans, and adjacent public sidewalk and road elements.
Discussion: This proposed standard prohibits vertical changes in level in other transitional areas such as flare/ramp, flare/sidewalk, ramp/landing, ramp/sidewalk, landing/sidewalk, and gutter/pavement. All connections must be flush, within reasonable construction tolerances.
Vertical changes in level at the base of curb ramps and landings , called "lips", have long been used to control drainage at curb ramps. However, since these lips create only a minimal vertical face, they are relatively ineffective in preventing storm water runoff in the gutter from impacting the curb ramp. When the front caster wheels of a wheelchair contacts a gutter lip, the caster wheels may be deflected and quickly stop the chair. Depending upon the velocity at the time of contact, the user may be thrown forward from the wheelchair. The degree of stormwater channelization provided by a drainage lip is not sufficient to offset the hazard it creates for pedestrians with disabilities.
Research need: Research is needed to develop design alternatives to minimize the adverse effect on wheelchair travel of surfaces that contain grade breaks.
X02.4.12 Detectable warnings.
Sidewalk/street transitions shall have a detectable warning complying with Section X02.5.7.
EXCEPTION: Detectable warnings shall not be provided where the sidewalk/street transition occurs at an unsignalized driveway.
Discussion: The committee recognized that some currently manufactured detectable warning products cannot be installed on warped surfaces or surfaces with grade breaks. The industry will need to accept the challenge to develop detectable warning surface materials that will be usable in non-planar applications.
X02.4.13 Vehicular obstructions.
Curb ramps and flush landings shall be located or protected so that legally parked vehicles do not obstruct the pedestrian access route.
Discussion: It was agreed that there is a need for a provision related to preventing the obstruction of the pedestrian access route by legally parked cars. The recommended provision is consistent with Interim Final Rule section 14.2.4. Public agencies should consider lengthening the no parking zone adjacent to a crosswalk, since wheelchair users and people of short stature may be hidden from a motorist's view by parked cars.
X02.4.14 Curb type. Reserved.
Frontier issue: The committee discussed and wishes to add the following proposal to the list of frontier issues: To aid in the protection of all pedestrians at intersection corners, and to make intersection geometry more cane detectable, the committee suggests that where rolled or "rollover" curb sections are proposed in new construction, a transition be provided from the rolled curb section to a barrier or vertical curb section of at least the same height and running the entire return of the curb return, and within 10 feet of the edge of each curb ramp (excluding flares) or the flush street transition.
X02.5 Pedestrian Street Crossings