### Detectable Warning Requirements

Detectable warnings on curb ramps have been in and out of the ADA/ABA
requirements for the past several years. The current requirement in
ABAAS is they are required at platform edges only.

However, The Access Board has a draft guideline for Public Rights of Way
(unofficial) which includes a requirement for a detectable warning
surface 2 feet deep [where the ramp, landing, or blended
transition]{.mark} [connects to a crosswalk]{.mark}.

The DSC design standard is to require the detectable warnings (truncated
domes) on curb ramps in walks that continue across a street. They are
not required at curb ramps in parking lots.

##### See: 

##### Revised Draft Guidelines for Accessible Public Rights-of-Way    

##### November 23, 2005: <http://www.access-board.gov/prowac/draft.htm>

**R221 Detectable Warning Surfaces**\
Detectable warning surfaces shall comply with R304.

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  *Advisory R221 Detectable Warning Surfaces. Detectable warning surfaces
  are required where curb ramps, blended transitions, or landings provide
  a flush pedestrian connection to the street. Sidewalk crossings of
  residential driveways should not generally be provided with detectable
  warnings, since the pedestrian right-of-way continues across most
  driveway aprons and overuse of detectable warning surfaces should be
  avoided in the interests of message clarity. However, where commercial
  driveways are provided with traffic control devices or otherwise are
  permitted to operate like public streets, detectable warnings should be
  provided at the junction between the pedestrian route and the street.*

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**R304 Detectable Warning Surfaces**

**R304.1 General.** Detectable warnings shall consist of a surface of
truncated domes aligned in a square or radial grid pattern and shall
comply with R304.

**R304.1.1 Dome Size.** Truncated domes in a detectable warning surface
shall have a base diameter of 23 mm (0.9 in) minimum to 36 mm (1.4 in)
maximum, a top diameter of 50 percent of the base diameter minimum to 65
percent of the base diameter maximum, and a height of 5 mm (0.2 in).

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  *Advisory R304.1.1 Dome Size. Where domes are arrayed radially, they
  may differ in diameter within the ranges specified.*

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**R304.1.2 Dome Spacing.** Truncated domes in a detectable warning
surface shall have a center-to-center spacing of 41 mm (1.6 in) minimum
and 61 mm (2.4 in) maximum, and a base-to-base spacing of 17 mm (0.65
in) minimum, measured between the most adjacent domes.

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  *Advisory R304.1.2 Dome Spacing. Where domes are arrayed radially, they
  may differ in center-to-center spacing within the range specified.*

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**R304.1.3 Contrast.** Detectable warning surfaces shall contrast
visually with adjacent gutter, street or highway, or walkway surfaces,
either light-on-dark or dark-on-light.

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  *Advisory R304.1.3 Contrast. Contrast may be provided on the full ramp
  surface but should not extend to the flared sides. Many pedestrians use
  the visual contrast at the toe of the ramp to locate the curb ramp
  opening from the other side of the street.*

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**R304.1.4 Size.** Detectable warning surfaces shall extend 610 mm (24
in) minimum in the direction of travel and the full width of the curb
ramp (exclusive of flares), the landing, or the blended transition.

**R304.2 Location and Alignment**

**R304.2.1 Perpendicular Curb Ramps.** Where both ends of the bottom
grade break complying with R303.3.4 are 1.5 m (5.0 ft) or less from the
back of curb, the detectable warning shall be located on the ramp
surface at the bottom grade break. Where either end of the bottom grade
break is more than 1.5 m (5.0 ft) from the back of curb, the detectable
warning shall be located on the lower landing.

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  *Advisory R304.2.1 Perpendicular Curb Ramps. Detectable warnings are
  intended to provide a tactile equivalent underfoot of the visible
  curbline; those placed too far from the street edge because of a large
  curb radius may compromise effective crossing analysis.*

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**R304.2.2 Landings and Blended Transitions.** The detectable warning
shall be located on the landing or blended transition at the back of
curb.

**R304.2.3 Alignment.** The rows of truncated domes in a detectable
warning surface shall be aligned to be perpendicular or radial to the
grade break between the ramp, landing, or blended transition and the
street.

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  *Advisory R304.2.3 Alignment. Where a ramp, landing, or blended
  transition provides access to the street continuously around a corner,
  the vertical rows of truncated domes in a detectable warning surface
  should be aligned to be perpendicular or radial to the grade break
  between the ramp and the street for a 1.2 meter-wide (4.0 ft) width for
  each crosswalk served.*

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**R304.2.3 Rail Crossings.** The detectable warning surface shall be
located so that the edge nearest the rail crossing is 1.8 m (6 ft)
minimum and 4.6 m (15 ft) maximum from the centerline of the nearest
rail. The rows of truncated domes in a detectable warning surface shall
be aligned to be parallel with the direction of wheelchair travel.

**R305 Pedestrian Crossings**

**R305.1 General.** Pedestrian crossings shall comply with R305.

**R305.2 Crosswalks.** Crosswalks shall comply with R305.2 and shall
contain a pedestrian access route that connects to departure and arrival
walkways through any median or pedestrian refuge island.

**R305.2.1 Width.** Marked crosswalks shall be 1.8 m (6 ft) wide
minimum.

**R305.2.2 Cross Slope**

**R305.2.2.1 Crossings with Stop Control.** The cross slope shall be 2
percent maximum.

**R305.2.2.2 Crossings without Stop Control.** The cross slope shall be
5 percent maximum.

**R305. 2.2.3 Midblock Crossings.** The cross slope at midblock
crossings shall be permitted to be warped to meet street or highway
grade.

**R305.2.3 Running Slope.** The running slope shall be 5 percent
maximum, measured parallel to the direction of pedestrian travel in the
crosswalk.

##### ABAAS: <http://www.access-board.gov/ada-aba/final.htm#pgfId-1006509>

##### 705 Detectable Warnings

705.1 General. Detectable warnings shall consist of a surface of
truncated domes and shall comply with 705.

705.1.1 Dome Size. Truncated domes in a detectable warning surface shall
have a base diameter of 0.9 inch (23 mm) minimum and 1.4 inches (36 mm)
maximum, a top diameter of 50 percent of the base diameter minimum to 65
percent of the base diameter maximum, and a height of 0.2 inch (5.1 mm).

705.1.2 Dome Spacing. Truncated domes in a detectable warning surface
shall have a center-to-center spacing of 1.6 inches (41 mm) minimum and
2.4 inches (61 mm) maximum, and a base-to-base spacing of 0.65 inch (17
mm) minimum, measured between the most adjacent domes on a square grid.

705.1.3 Contrast. Detectable warning surfaces shall contrast visually
with adjacent walking surfaces either light-on-dark, or dark-on-light.

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  ![](media/image1.png){width="6.290972222222222in"
  height="1.7604166666666667in"} 

  **Figure 705.1 Size and Spacing of Truncated Domes**
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705.2 Platform Edges. Detectable warning surfaces at platform boarding
edges shall be 24 inches (610 mm) wide and shall extend the full length
of the public use areas of the platform.

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