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Chapter 3 - United States Acc—Board P ge 5 of 12 <br /> blended transitions,landings,and gutter areas within the pedestrian access <br /> route. Surface slopes that meet at grade breaks shall be flush. <br /> R303.3.5 Counter Slopes.The counter slope of the gutter or street at the <br /> foot of a curb ramp,landing,or blended transition shall be 5 percent <br /> maximum. <br /> R303.3.6 Clear Space.Beyond the curb face,a clear space of 1.2 m(4.0 <br /> ft)minimum by 1.2 m(4.0 ft)minimum shall be provided within the width <br /> of the crosswalk and wholly outside the parallel vehicle travel lane. <br /> R304 Detectable Warning Surfaces <br /> 8304.1 General. Detectable warnings shall consist of a surface of <br /> truncated domes aligned in a square or radial grid pattern and shall comply <br /> with R304. <br /> R304.1.1 Dome Size.Truncated domes in a detectable warning surface <br /> shall have a base diameter of 23 mm(0.9 in)minimum to 36 mm(1.4 in) <br /> maximum,a top diameter of 50 percent of the base diameter minimum to <br /> 65 percent of the base diameter maximum,and a height of 5 mm(0.2 in). <br /> Advisory R304.1.1 Dome Size. Where domes are arrayed radially,they may <br /> differ in diameter within the ranges specified. <br /> R304.1.2 Dome Spacing.Truncated domes in a detectable warning <br /> surface shall have a center-to-center spacing of 41 mm(1.6 in)minimum <br /> and 61 mm(2.4 in)maximum,and a base-to-base spacing of 17 mm(0.65 <br /> in)minimum,measured between the most adjacent domes. <br /> Advisory 8304.1.2 Dome Spacing. Where domes are arrayed radially,they <br /> may differ in center-to-center spacing within the range specified. <br /> R304.1.3 Contrast.Detectable warning surfaces shall contrast visually <br /> with adjacent gutter,street or highway,or walkway surfaces,either light-on <br /> -dark or dark-on-light. <br /> Advisory R304.1.3 Contrast. Contrast may be provided on the full ramp <br /> surface but should not extend to the flared sides.Many pedestrians use the <br /> visual contrast at the toe of the ramp to locate the curb ramp opening from <br /> the other side of the street. <br /> R304.1.4 Size.Detectable warning surfaces shall extend 610 mm(24 in) <br /> minimum in the direction of travel and the full width of the curb ramp <br /> (exclusive of flares),the landing,or the blended transition. <br /> R304.2 Location and Alignment <br /> R304.2.1 Perpendicular Curb Ramps.Where both ends of the bottom <br /> grade break complying with R303.3.4 are 1.5 m (5.0 ft)or less from the <br /> back of curb,the detectable warning shall be located on the ramp surface at <br /> the bottom grade break.Where either end of the bottom grade break is <br /> more than 1.5 m(5.0 ft)from the back of curb,the detectable warning <br /> shall be located on the lower landing. <br /> Advisory R304.2.1 Perpendicular Curb Ramps.Detectable warnings are <br /> intended to provide a tactile equivalent underfoot of the visible curbline; <br /> those placed too far from the street edge because of a large curb radius <br /> may compromise effective crossing analysis. <br /> R304.2.2 Landings and Blended Transitions.The detectable warning <br /> shall be located on the landing or blended transition at the back of curb. <br /> R304.2.3 Alignment.The rows of truncated domes in a detectable <br /> warning surface shall be aligned to be perpendicular or radial to the grade <br /> break between the ramp,landing,or blended transition and the street. <br /> Advisory R304.2.3 Alignment. Where a ramp,landing,or blended transition <br /> provides access to the street continuously around a corner,the vertical rows <br /> http://www.access-board.gov/guidelines-and-standards/streets-sidewalks/public-rights-of-... 12/15/2014 <br />