Sidewalk Static Obstructions and Their Impact on Clear Width

Abstract

Data on sidewalks have long been deficient. But advances in remote sensing are beginning to increase data prevalence and accuracy. These sidewalk datasets rarely, if ever, account for static obstructions in the sidewalk such as signs, street furniture, or trees. This paper seeks to determine how much of a difference accounting for static obstructions will make when measuring the clear width of sidewalks. We extracted the minimum width of sidewalk surfaces—both with and without accounting for static obstructions—for the entirety of Cambridge, MA, using new GIS methods described in this paper. We then compared these results against Americans with Disabilities Act (ADA) standards for clear width as well as national and federal sidewalk guidelines. The results suggest a significant decrease in the average clear width of sidewalks when accounting for static obstructions. More specifically, the clear width of the average sidewalk drops from 4.5 ft (1.4 m) to 3.5 ft (1.1 m). The percentage of sidewalk segments meeting the 3-ft ADA standard drops from 78% to 51% when accounting for static obstructions. For the proposed 4-ft (1.2-m) ADA standard, it plunges from 59% of sidewalk segments meeting the width threshold to 31%. These results demonstrate that not accounting for static obstructions could lead to a gross overestimation of seemingly adequate sidewalks and an unrealistic assessment of sidewalk infrastructure and pedestrian accessibility.

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“…A study conducted in Cambridge, MA, for example, evaluated ADA conditions of sidewalks and found that nearly half of all sidewalks within the city did not meet the minimum 36-in. width ADA standard ( 30 ).…”