Here’s what Wayne Stuart wrote: The State of California requires that I provide a contrasting color warning surface, but I can’t find the light reflectance value (LVR) of typical grey concrete as referenced in:

11B-705.1.1.3 Color and Contrast. Detectable warning surfaces at transit boarding platform edges, bus stops, hazardous vehicular areas, reflecting pools, and track crossings shall comply with Section 11B-705. Detectable warnings at other locations shall comply with either Section 11B-705. or Section 11B-705. The material used to provide visual contrast shall be an integral part of the surface.

  • 11B-705. Detectable warning surfaces shall be yellow and approximate FS 33538 of Federal Standard 595C.
  • 11B-705. Detectable warning surfaces shall provide a 70 percent minimum visual contrast visually with adjacent walking surfaces. Contrast in percent shall be determined by:

Contrast percent = [(B1-B2)/B1] x 100 where

  • B1 = light reflectance value (LRV) of the lighter area and
  • B2 = light reflectance value (LRV) of the darker area.

As far as I can tell, this requirement became effective on July 1. If you have any guidance, e-mail Tell Wayne I sent you.

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