The use of sensors within and across a city such as New York offers rapidly expanding possibilities to generate data on urban challenges such as wheelchair accessibility. Streetscape accessibility is an inherently physical and three-dimensional phenomenon for which elevation and slope, structural properties such as cracking of concrete, and design considerations such as orientation of cross-walks with regard to traffic are all relevant. These dimensions of the challenge make it amenable to urban data collection approaches, from GIS-based surveying with human input to 3D imaging using LiDAR. Moreover, streetscape accessibility is a challenge conditioned by limited budgets of organisations such as the city’s Department of Transport. Given the high costs of traditional data collection methods such as sending teams of surveyors to street corners, substantial benefit could be attained from sensing modalities that harness volunteer manpower to acquire data. Expected deployment of 3D imaging technologies in the 2019 release of the iPhone provides another motivation \cite{webb2017}.
1.2 ADA standards
Recognizing the importance of accessible streets to wheelchair users and others with mobility impairments, the Americans with Disabilities Act (ADA) sets out detailed standards for Departments of Transport as well as building owners to abide by (www.ada.gov). A key provision in the ADA concerns curb cuts. Where sidewalks meet an intersection, or a pedestrian crossing exists, the ADA mandates that the sidewalk surface be cut away in a smooth ramp that leads to the street with suitable width and a sufficiently shallow incline. However, while the ADA is widely recognized as a legislative advance, disability rights groups complain that it goes un-implemented, with many street corners posing insuperable obstacles to their users. Wheelchair users or the visually impaired can be blocked or endangered by, among other things: sudden drop-offs, crumbling and uneven concrete, curb cuts that lead directly into oncoming traffic at the center of an intersection. The ADA also mandates detectable warnings such as stripes or bumps in the curb ramp surface, which are frequently lacking or eroded.
1.3 State of accessibility in NYC