During the night and early morning, it had snowed. It was the first snow of the season, and there was about an inch of snow on the ground. As DW walked down the street, he saw a recently constructed curb cut. It appeared to be free of snow and ice. The owner of the adjoining property had earlier shoveled the sidewalk. According to DW, as he stepped onto the flared side of the curb cut, his feet suddenly slid from beneath him, and he fell backward onto the pavement.

HF Issue: Did the flared side of the curb cut pose an unreasonable slipping hazard?

HF Investigation: Information collected included, but was not limited to, DW's height and weight; the slopes of the sidewalk and curb cut; the static coefficient of friction (COF) of the pavement; the shoes that DW was wearing at the time of the fall.

Analysis: A scale 3D computer model of the sidewalk, curb cut, and of DW was generated. The slope of the flared side of the ramp ranged between 15 and 20 degrees.

For purposes of comparison, a computer model of a "standard" curb ramp with a maximum side slope of 1:6 or about 9.5 degrees was created.

Analysis involved establishing the requisite COF between footwear and the sloped pavement in order for the surface to provide adequate resistance to the foot sliding forward at heel-strike.

A sloped surface must have a higher COF with footwear than a level surface to provide the same level of slip resistance.

The risk of slipping increases when the adherence characteristics of a surface change for

the worse, but the individual maintains the same length of stride.