Curb ramp flare slope requirements cap the sloped sides of a curb ramp at 1:10 (10 percent) under both the 2010 ADA Standards and the 2023 Public Right-of-Way Accessibility Guidelines. That ratio tightens to 1:12 (8.3 percent) when the sidewalk behind the ramp is less than 48 inches deep, because wheelchair users end up maneuvering across the flares themselves instead of on a flat landing. Slope is measured along the flare surface, parallel to the curb line.
When Flares Are Actually Required
A common misconception is that every curb ramp needs flared sides. The 2010 ADA Standards don’t require them. Section 406.3 only caps the slope at 1:10 “where provided.”1U.S. Access Board. Chapter 4: Ramps and Curb Ramps Install flares and you have to get the slope right; skip them and the ADA Standards alone don’t force the issue.
The 2023 PROWAG final rule is stricter. Section R304.2.6 requires flared sides wherever a pedestrian circulation path crosses the side of a curb ramp, with a slope of 1:10 maximum measured parallel to the curb line.2U.S. Access Board. R3: Technical Requirements Because most curb ramps sit in the public right-of-way, PROWAG is the standard that controls in practice. If people are walking along a sidewalk and their route crosses the side of the ramp, flares are mandatory.
The only time flares can be skipped entirely is when something physically prevents pedestrians from walking across the side of the ramp: a grass strip, a continuous planter, a railing. In those situations, returned curbs (vertical sides that drop straight to the adjacent surface) are acceptable. A small planter or a row of decorative stones doesn’t count. The obstruction has to be immovable and substantial enough that no one would try to cross the ramp side.3ADA.gov. ADA Accessibility Survey Instructions: Curb Ramps Using returned curbs where pedestrians actually walk creates a sharp vertical edge and a tripping hazard.
The 1:10 Rule
Where flares are provided, the slope cannot exceed 1:10.1U.S. Access Board. Chapter 4: Ramps and Curb Ramps For every ten inches of horizontal run, the surface can drop no more than one inch. That gradient is shallow enough that a pedestrian stepping onto the side of the ramp won’t lose balance, and a wheelchair user who drifts slightly off the main ramp run won’t tip sideways.
Contractors routinely pour flares steeper than 1:10 without realizing it. A flare that measures 12 or 13 percent doesn’t look dangerous when you’re standing over wet concrete, but it fails inspection and creates a real tipping risk. The measurement runs along the surface of the flare, parallel to the curb line, from the top of the ramp down to where the flare meets sidewalk grade.2U.S. Access Board. R3: Technical Requirements
When the Slope Tightens to 1:12
Sometimes there isn’t enough room at the top of a curb ramp for a full landing. In alterations where the sidewalk behind the ramp is less than 48 inches deep, wheelchair users end up maneuvering partly on the flares themselves. When that happens, the flare slope maximum drops to 1:12 (8.3 percent).3ADA.gov. ADA Accessibility Survey Instructions: Curb Ramps
The reason matters. At a ramp with a full 36-inch-deep landing, flares are mainly a tripping safeguard for people walking past, and wheelchair users complete their turn on the flat landing. Shrink the landing below 48 inches and the wheelchair user is forced to negotiate the flares during the turn. A 10 percent cross-slope in the middle of that maneuver is steep enough to cause a tip-over, so the gentler 1:12 grade applies.1U.S. Access Board. Chapter 4: Ramps and Curb Ramps
Verify the sidewalk width during design. This single measurement determines which slope ratio governs. The top landing itself must be at least 36 inches deep and at least as wide as the ramp; the 48-inch trigger for tighter flares is about whether the sidewalk behind provides enough space for a wheelchair user to turn without touching the flare.1U.S. Access Board. Chapter 4: Ramps and Curb Ramps
How Landing Slope Interacts
The landing at the top of the ramp isn’t the flare, but the two have to work together. Where the connecting accessible route runs perpendicular to the ramp, the landing cross-slope is capped at 1:48 (about 2 percent). Where the route runs parallel to the ramp, the landing can slope up to 1:20 (5 percent).1U.S. Access Board. Chapter 4: Ramps and Curb Ramps Exceed those limits and the landing effectively becomes an extension of the ramp surface, which is the same problem the flare slope rules exist to prevent: a wheelchair user turning on ground that isn’t flat.
Measuring Flare Slope in the Field
A flare can look fine and still fail. Eyeballing concrete slopes is unreliable, which is why inspectors use a digital inclinometer, commonly called a smart level. The standard tool is a 24-inch model placed directly on the flare surface. Before each session, calibrate the device on a flat surface so that direct and reverse readings at the same position agree within 0.2 percent.
Proper technique involves taking both a direct reading and a reverse reading (rotating the device 180 degrees) at the same spot, then averaging the two. That cancels out systematic instrument error. Work across the flare in a grid with roughly 18-inch spacing to find the steepest point, because the maximum slope anywhere on the flare determines compliance. If the steepest reading exceeds 1:10, or 1:12 for a constrained landing, the flare fails no matter what the average measures. Checking only the center of the flare is how contractors get surprised at inspection.
What a Failed Flare Costs
Non-compliant curb ramps can trigger enforcement through two paths. State and local government infrastructure falls under Title II of the ADA, enforced by the U.S. Department of Justice. Private facilities open to the public fall under Title III. In both cases, individuals can file DOJ complaints or bring private lawsuits seeking injunctive relief, meaning a court order to fix the problem.4ADA.gov. Americans with Disabilities Act Title III Regulations
For Title III violations, the DOJ can seek civil penalties through the courts. As of mid-2025, the inflation-adjusted maximums are $118,225 for a first violation and $236,451 for subsequent violations, and those figures rise periodically with inflation adjustments.5eCFR. 28 CFR 85.5 – Adjustments to Penalties Private plaintiffs in Title III cases can obtain compliance orders but generally cannot recover monetary damages in federal court. For most property owners, the real financial hit isn’t the penalty. It’s tearing out and re-pouring the concrete, often under a court-imposed deadline, because a flare slope can’t be shaved down after the fact. Getting the 1:10 (or 1:12) right the first time is the only economical option.