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R303.3.6 Clear Space. Beyond the curb face, a clear space of 1.2 m (4.0 ft) <br />minimum by 1.2 m (4.0 ft) minimum shall be provided within the width of the <br />crosswalk and wholly outside the parallel vehicle travel lane. <br />R304 Detectable Warning Surfaces <br />R304.1 General. Detectable warnings shall consist of a surface of truncated domes <br />aligned in a square or radial grid pattern and shall comply with R304. <br />R304.1.1 Dome Size. Truncated domes in a detectable warning surface shall <br />have a base diameter of 23 mm (0.9 in) minimum to 36 mm (1.4 in) maximum, a <br />top diameter of 50 percent of the base diameter minimum to 65 percent of the <br />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 differ in <br />diameter within the ranges specified. <br />R304.1.2 Dome Spacing. Truncated domes in a detectable warning surface shall <br />have a center -to -center spacing of 41 mm (1.6 in) minimum and 61 mm (2.4 in) <br />maximum, and a base -to -base spacing of 17 mm (0.65 in) minimum, measured <br />between the most adjacent domes. <br />Advisory R304.1.2 Dome Spacing. Where domes are arrayed radially, they may differ in <br />center -to -center spacing within the range specified <br />R304.1.3 Contrast. Detectable warning surfaces shall contrast visually with <br />adjacent gutter, street or highway, or walkway surface, either light -on -dark or <br />dark -on -light. <br />Advisory R304.1.3 Contrast. Contrast may be provided on the. full ramp surface but <br />should not extend to the flared sides. Many pedestrians use the visual contrast at the toe <br />of the ramp to locate the curb ramp opening from 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 (exclusive <br />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 grade <br />break complying with R303.3.4 are 1.5 m (5.0 ft) or less from the back of curb, <br />the detectable warning shall be located on the ramp surface at the bottom grade <br />break. Where either end of the bottom grade break is more than 1.5 m (5.0 ft) <br />from the back of curb, the detectable warning shall be located on the lower <br />landing. <br />37 <br />