ADA curb ramp slope, width, and landing

Build a curb ramp as a connected route

A curb ramp is a short ramp that transitions between a sidewalk and a street, parking area, or other lower surface. Its accessibility depends on more than the steepness of the ramp face. The running slope, cross slope, top landing, adjoining gutter, grade breaks, width, flares, and location must work together. The 2010 ADA Standards Section 406 refers to several ramp requirements in Section 405, so verify the full assembly.

For a new curb ramp, the running slope generally cannot be steeper than 1:12, and the cross slope cannot be steeper than 1:48. The adjoining gutter or road surface immediately at the bottom has a maximum counter slope of 1:20. Changes in level at the transition are not allowed. These limits prevent an abrupt break where a wheelchair front caster can catch or where the chair may tip backward.

Width and top landing

The curb ramp’s clear width is at least 36 inches, subject to applicable route and project requirements. A top landing is required so users can maneuver to and from the ramp without being forced to cross a sloped flare. The landing must be at least 36 inches long in the direction of the ramp run and at least as wide as the ramp, excluding flared sides. Confirm the landing remains clear after railings, signs, poles, and street furniture are installed.

Where the landing connects to a perpendicular accessible route, the cross slope of that route can constrain the landing slope. A top landing must not become a small tilted platform that drains water into the ramp or crosswalk. Check finished elevations at both sides and across the walking direction. The grade break at the top and bottom should be perpendicular to the ramp run to avoid compound slope and uneven wheel contact.

Flares and side protection

Where curb ramp flares are provided, their slope is limited to 1:10 under the cited ADA Standards. Flares are transitions at the sides, not part of the clear ramp width. They should be arranged so pedestrians do not encounter a sharp drop or confusing slope. A ramp with returned sides may be appropriate where pedestrian travel across the sides is discouraged, but the top landing requirement still applies.

The side flare and curb ramp must not project into a vehicular lane, parking space, or access aisle. At a marked crossing, the ramp must be contained within the crosswalk markings, excluding its flares. Diagonal ramps at corners have special clear-space and alignment provisions. A ramp that is technically the right slope but directs a wheelchair into traffic is not a workable accessible route.

Construction tolerances and drainage

Concrete placement can leave a ramp steeper or more twisted than the drawings. Use a digital level or calibrated slope-measuring tool to verify both running and cross slopes after curing. Measure along the intended direction of travel and perpendicular to it. Do not use one diagonal measurement to infer both. Check near the top and bottom, where transitions and concrete finishing commonly introduce lips or abrupt grade changes.

The landing and ramp must drain without ponding. Water can collect at a gutter transition, low point, or landing where grades were not coordinated. A drainage inlet or grate should not create an inaccessible opening or level change. If site grading forces a different elevation, revise the ramp and adjoining surfaces together with design approval rather than steepening one segment in the field.

Example: a curb ramp at a marked crossing

A sidewalk meets a street at a marked crosswalk. The curb ramp is 36 inches wide, rises 6 inches over 72 inches of horizontal run, and has a cross slope measured at 1:48. The running slope is 1:12. The crew then checks that the top landing is at least 36 inches long and ramp-width, the bottom counter slope is no steeper than 1:20, and the ramp opening is contained within the marked crossing. The flares remain outside the clear width.

If a utility pole sits in the landing, the route may fail even though the ramp dimensions are correct. If a gutter creates a 1:12 counter slope, the transition also fails the 1:20 maximum. Correct the grading and obstacle placement as an integrated detail. Before final acceptance, measure the completed surface and verify it drains while preserving the accessible route.

Common mistakes and exam cues

Common mistakes include confusing cross slope with running slope, measuring ramp length along the surface instead of horizontal run when calculating slope, omitting the top landing, and treating the flare as part of the 36-inch clear width. Another error is ignoring the street counter slope or allowing the ramp to project into an access aisle. For questions, identify each surface separately and apply the correct limit.

The ADA Standards permit steeper slopes in some existing-site alterations when space is constrained, within narrow limits tied to maximum rise. Do not apply those exceptions to new construction or assume that a steep field condition qualifies. Determine whether the project is new construction or alteration and consult the adopted standard and applicable public-right-of-way requirements.

Quick review

• New curb ramps generally have a 1:12 maximum running slope and 1:48 maximum cross slope.
• Top landing: at least 36 inches long and at least as wide as the ramp.
• Adjoining counter slope: no steeper than 1:20.
• Flares, if provided, are no steeper than 1:10.
• Keep the ramp and landing out of vehicle lanes, parking spaces, and access aisles; inspect the finished surface and drainage.