SDOT recently presented to the Northwest Universal Design Council on features that make an intersection accessible to all pedestrians. One topic was the complexity of curb ramp design, especially in Seattle where the hills and terrain can create some significant challenges.
Curb ramp construction is not a simple process where a contractor simply builds a sloped ramp; it takes an engineer much time and effort to figure out how to build a ramp that meets design standards, and is usable to pedestrians while addressing potential site constraints.
The first item that may be considered: what makes the most sense for curb ramp installation and crosswalk alignment at an existing intersection.
Aerial View of Intersection to be Improved
Existing crossings that are generally parallel to the curb lines are shown in red. Due to the dramatic skew of the intersection, crossings would be very long. After review by a traffic engineer, a better location for curb ramps was found that would accommodate much shorter crossings, shown in green.
Before design can begin, it is likely necessary for a surveyor to visit the location to provide dimensional information and identify any potential conflicts within the area, such as trees or utility structures. This information can then be put into computer aided-design (CAD), which provides a 3-dimensional image so the designer can begin planning the curb ramp.
At this particular corner, the designer is faced with a number of challenges – the most daunting being the heavy roadway slope.
Steep Roadway Slopes and Limited Available Right of Way
Knowing the elevations of the curb, the designer can determine if it is possible to construct a ramp that satisfies all of the design criteria. If not, it is SDOT’s responsibility to construct a ramp that is accessible and usable to the maximum extent feasible (MEF).
When the designer has determined the best possible design given the existing site conditions, the CAD drawing is completed, printed, and distributed to the contractor for construction. 
While there is no shortage of challenges when building curb ramps, SDOT, contractors, and the community work together to construct an accessible pedestrian network for all.
If you have any questions about accessibility within the Seattle public right-of-way, we encourage you contact SDOT’s ADA Coordinator, Michael Shaw. He can be reached at (206) 615-1974 or by email at Michael.Shaw@seattle.gov.