Accessibility is one of the many topics featured on the California Supplemental Exam for landscape architects. California adopted the Americans with Disability Act 2010 standards in the 2013 edition of the California Building Code. This article shows you where detectable warning surfaces are needed and discusses the minimum and maximum dimensions for the warning surface.
What is a Detectable Warning Surface?
According to the “2013 California Building Code Advisory Manual”, detectable warning surfaces are “a standardized surface feature built in or applied to walking surfaces or other elements to warn of hazards on a circulation path.”
“Detectable warnings are provided for the benefit of persons with visual impairments to indicate transitions to potentially hazardous areas.”
Why Are Detectable Warning Surfaces Necessary?
Curbs are the normal warning cue to visually impaired individuals that there is vehicle traffic ahead. “Curbs can be used by pedestrians with vision impairments to detect the boundary between a sidewalk and a vehicular way.”
When there is a curb in the accessible route of travel, the normal curb cue is removed and a potentially hazardous condition occurs.
“Curb ramps remove the needed cues for persons with visual impairments; detectable warnings have been developed as a replacement cue and warning to indicate the presence of a vehicular way.”
Where are Detectable Warning Surfaces Required?
Detectable warnings shall be provided where required for the following situations:
- Platform edges
- Curb ramps
- Islands or cut-through medians
- Bus stops
- Hazardous vehicular areas
- Reflecting pools
- Track crossings
Now let’s examine each location which needs a detectable warning surface in greater detail.
Detectable warning surfaces at platform boarding edges shall be 24 inches wide and shall extend the full length of the public use areas of the platform.
Detectable warnings at curb ramps shall extend 36 inches in the direction of travel. Detectable warnings shall extend the full width of the ramp run excluding any flared sides. Detectable warnings shall be located so the edge nearest the curb is 6 inches minimum and 8 inches maximum from the line at the face of the curb marking the transition between the curb and the gutter, street or highway.
On parallel curb ramps, detectable warnings shall be placed on the turning space at the flush transition between the street and sidewalk.
Islands or Cut-through Medians
Detectable warnings at pedestrian islands or cut-through medians shall be 36 inches minimum in depth extending the full width of the pedestrian path or cut-through, placed at the edges of the pedestrian island or cut-through median, and shall be separated by 24 inches minimum of walking surface without detectable warnings.
However, there is an exception for pedestrian islands that are less than 8 feet in length. Detectable warnings shall be 24 inches minimum in depth at pedestrian islands or cut-through medians that are less than 96 inches in length in the direction of pedestrian travel.
When detectable warnings are provided at bus stop pads, it shall be 36 inches in width. If a square curb is not provided at a bus stop, a detectable warning surface is required.
**Hazardous Vehicular Areas **
If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning. Detectable warnings at hazardous vehicular areas shall be 36 inches in width.
The edges of reflecting pools shall be protected by railings, walls, warning curbs or detectable warnings. When detectable warnings are provided at reflecting pools, it shall be 24 inches minimum and 36 inches maximum in width.
Where it is necessary to cross tracks to reach transit boarding platforms, detectable warnings shall be provided; at transit boarding platforms, the pedestrian access shall be identified with a detectable directional texture. Detectable warnings at track crossings shall be 36 inches in the direction of pedestrian travel and extend the full width of the circulation path.
Characteristics Of A Detectable Warning Pattern
The detectable warning surface must have certain characteristics to meet ADA regulatory requirements and California state guidance from the Division of State Architect. The warning surface must have the following qualities
- Dome size
- Dome spacing
Dome size — Truncated domes in a detectable warning surface shall have a base diameter of 0.9 inch minimum and 0.92 inch maximum, a top diameter of 0.45 inch minimum and 0.47 inch maximum, and a height of 0.18 inch minimum and 0.22 inch maximum.
Dome spacing — Truncated domes in a detectable warning surface shall have a center-to-center spacing of 2.3 inches minimum and 2.4 inches maximum, and a base-to-base spacing of 0.65 inch minimum, measured between the most adjacent domes on a square grid. Where the domes are installed in a radial pattern, the truncated domes shall have a center-to-center spacing of 1.6 inches minimum to 2.4 inches maximum.
Contrast — Detectable warning surfaces shall contrast visually with adjacent walking surfaces either light-on-dark, or dark-on-light. The material used to provide contrast shall be an
integral part of the surface.
Contrast shall be determined by the following formula:
Contrast = [(B1-B2)/B1] x 100 percent
B1 = light reflectance value (LRV) of the lighter area and
B2 = light reflectance value (LRV) of the darker area.
However, where the detectable warning surface does not adequately contrast with adjacent surfaces, a 1 inch wide black strip shall separate yellow detectable warning from adjacent surfaces.
Resiliency — Detectable warning surfaces shall differ from adjoining surfaces in resiliency or sound-on-cane contact.
There is an exception to the resiliency requirement for warning surfaces on curb ramps and similar situation. “Detectable warning surfaces at curb ramps, islands or cut-through medians shall not be required to comply” with the resiliency standard.
Color — Detectable warning surfaces shall be yellow conforming to FS 33538 of Federal Standard 595C.
Just like with resiliency, there is an exception for curb ramps. Detectable warning surfaces at curb ramps, islands or cut-through medians shall not be required to comply with the color standard and may be made of other materials.
Detectable warning surfaces are used to indicate hazardous intersections to visually impaired site uses by creating a texture that feels and sounds different that the surrounding surface. Provide detectable warning surfaces of a proper size and characteristics where they are required by regulation. As a general rule of thumb, a detectable warning surface is required where pedestrian traffic meets vehicular traffic.
The quotes and information in the article came from the 2013 California Building Code Advisory Manual. “This document contains the 2013 CBC accessibility provisions adopted by DSA and commentary on selected requirements. Commentary is included from the 2010 ADA Standards for Accessible Design and from DSA for provisions unique to California. Additionally, an expanded table of contents for Chapter 11B is provided at the beginning of the chapter.”
You can download the document [here].