abstract background black bumps caution coloured design equipment floor grunge health no non non-skid non-slip object occupational outdoor outside pad pads path pathway pattern pavers paving plastic prevent prevention rubber safety shape shiny sidewalk skid slip slipping stone street surface texture traction used walkway Dirt yellow coarse diamond plate diamondplate industrial iron metal non skid plate rough rust San Francisco steel urban ba1969 grid rustic rusty blur bump tiles New York nubs NYC subway threshold cover oxide ridges age aged grit Portland surace weathered asphalt diamond-plate construction diamond metallic oxidation rusting bump map decay