For most people, the short steps from sidewalk to street and across to the other side take little or no thought. But if you’re in a wheelchair, the journey requires extensive investigation and planning. Regularly placed, properly designed curb ramps — or the lack thereof — make the difference between safely navigating an intersection or having to go outside normal travel routes to find a suitable crossing.
According to the U.S. Census Bureau, more than 3.3 million people use a wheelchair or other mobility device. San Francisco began installing wheelchair-friendly curb ramps in the early 1970s, well before the Americans with Disabilities Act (ADA) went into effect on Jan. 1, 1991. Of the city’s 28,000 street corners, two-thirds have at least one ramp. In addition to adding a ramp to intersections that don’t have one, the San Francisco Department of Public Works is systematically replacing the original ramps because they don’t meet federal design requirements. This monumental effort is expected to be completed by 2017 for about $1 million/year (see table on next page for timeline).
“The original ramps’ cookie-cutter design wasn’t engineered to meet the specifications that are now required,” says Suzanne Levine, a GIS specialist for the department’s Curb Ramp Group, referring to amendments that became effective on May 24, 2011. “In addition, we also have to consider the city’s unique geography and existing infrastructure.”
The law’s design requirements permit curb ramps to slope up to 10% if space limitations don’t allow for the required 1:12 angle. Even so, the city’s extremely hilly terrain makes compliance a challenge. In addition, there are basements directly under the sidewalks in some areas of the downtown districts, and their roofs could easily be damaged during ramp construction.
In 2000, Levine’s group retained Towill Inc. of Concord, Calif., to help develop a dual-purpose Curb Ramp Information System (CRIS) that provides the foundation for a curb-ramp map the public can access on the city’s website as well as an asset-management tool for infrastructure managers. The surveying and mapping consulting firm formulated initial data collection and processing procedures for the system, which is built on Esri’s ArcGIS.
Prioritizing ramp construction
The online map shows which of the city’s 28,000 street corners have a curb ramp. Each ramp is color-coded according to its condition score, which is calculated from physical attributes such as slope and cross slope at the ramp’s top and bottom landings. The measurements are determined by visual inspections by field engineers armed with digital levels and measuring tapes. The inspections are ongoing and the collected data is regularly uploaded into the system.
The public works department uses the system to track the progress of projects related to the city’s Americans with Disabilities Act Transition Plan for Curb Ramps and Sidewalks. The geodatabase records location inventory attributes, project design and construction milestones, and resident requests. Because the department tries to coordinate curb-ramp construction with larger street projects to save time and costs and minimize resident inconvenience, the geodatabase also links ramps approved for construction to their related public works project number.
The department prioritizes construction of new ramps based on criteria developed by the San Francisco Mayor’s Office on Disability: requests from a person with a disability, the condition score of existing ramps in the immediate area, and the proximity of the proposed ramp to government facilities such as health clinics, schools, parks, and public transportation.
An ADA-compliant ramp must meet not only the needs of those that use wheelchairs but also the needs of other people, whether or not they have physical disabilities. There are very different considerations for those with visual impairments, for example, who rely on the curb to help them identify the transition between the sidewalk and the street. In addition, the location and characteristics of the existing sidewalk and its relationship to the roadway it borders, including slope and drainage, affect ramp design and construction.
As a result, managers analyze each proposed ramp before issuing the work order. Levine hopes to use the geodatabase more in the decision-making process by creating a prioritization model using the weighted condition score of each ramp in relationship to buffers she’ll generate at varying distances around the intersections near buildings and transportation depots. A buffer is a GIS function that allows the creation of perimeters at specified distances from a point of interest so that spatial analyses can be performed.
“ArcGIS is a very useful tool in the prioritization process and could conceivably provide cost savings,” says Levine. She also wants to use the geodatabase to enable the online map to provide turn-by-turn directions for residents and visitors with mobility challenges.
—Baumann (email@example.com) is a writer for Esri (www.esri.com) in Redlands, Calif.
In addition to feedback from the public, San Francisco’s Americans with Disabilities Act Transition Plan for Curb Ramps and Sidewalks prioritizes new curb ramp construction and reconstruction by, in descending order:
1) Poor condition score and corners with no curb ramps
2) Locations that have only one ramp but where two directional ramps could feasibly fit
3) Where construction poses extreme difficulty, either because of physical constraints or legal complications such as privately owned subsidewalk basements
4) Ramps built to code at time of installation and that remain safe and usable, even if not up to current design standards. Photo: San Francisco Department of Public Works