Sidewalks and streets are designed to dimensions that come from how people actually move, not from what fits on the plan. The standards are specific, and they are the difference between a route that works for everyone and one that works for some.
Five feet of clear width is the working minimum for a pedestrian route, allowing two people to pass and a wheelchair to turn. Where a walk must narrow to four feet, passing spaces at least five feet wide are provided at regular intervals. Clear width is measured free of poles, hydrants, signs, and planters — obstructions in the middle of a walk are the most common accessibility failure in a streetscape.
Cross slope stays at or below two percent. Running slope should follow the adjacent roadway grade; where a walk is independent of a street, anything over five percent becomes a ramp and requires landings and handrails. Landings at doors, ramps, and curb ramps stay under two percent in all directions.
Every crossing needs a ramp with a running slope no steeper than 1:12, flared sides where pedestrians may walk across them, and a level landing at the top. Detectable warning surfaces — the truncated dome panels — mark the boundary between the walk and the street for pedestrians with vision impairments and are set back from the curb line as the standard specifies.
Vertical changes over a quarter inch must be beveled; over half an inch, ramped. Gaps in grates and joints are limited so wheels and canes do not catch. A route is only as accessible as its worst few feet.
Lane widths, turning radii, and sight distance at intersections and driveways follow the local street standards and AASHTO guidance. Corner radii in particular are a trade-off: a larger radius helps trucks turn and lengthens every pedestrian crossing at that corner.
These dimensions are not arbitrary. Each one traces back to a person trying to get somewhere safely.