4.3 Curb Ramps, Blended Transitions, and Detectable Warnings at Crossings
Key Takeaways
Curb ramp runs and blended transitions are 48 inches minimum wide, excluding flared sides (A117.1-2017 406.5.1).
Perpendicular curb ramps need a 48 x 48 inch top landing (48 x 60 where constrained at the back of sidewalk); parallel curb ramps need a 48 x 48 inch bottom landing (48 x 60 where constrained on two or more sides).
Curb ramp running slope is 1:20 minimum to 1:12 maximum, but the run need not exceed 15 feet; blended transitions are 1:20 maximum.
Cross slope is 1:48 maximum, counter slope at the gutter is 1:20 maximum, and flared sides are 10 percent maximum where pedestrians cross the ramp.
Detectable warnings are required at curb ramps and blended transitions at pedestrian street crossings, refuge islands, at-grade rail crossings and unprotected transit platform edges.
4.3 Curb Ramps, Blended Transitions, and Detectable Warnings at Crossings
Curb ramps are part of the Walking Surfaces and Ramps subtopic. ICC A117.1-2017 replaced the older curb ramp rules with a structure based on public right-of-way practice. If you learned curb ramps from the 2009 edition or the ADA Standards (36-inch width, 36-inch top landing, 1:10 flares), relearn them here.
Definitions
- Curb ramp: A short ramp cutting through a curb or built up to it.
- Blended transition: A raised pedestrian street crossing, depressed corner or similar connection between the pedestrian access route at sidewalk level and the street crossing, with a grade of 1:20 or less.
- Counter slope: Any slope opposing the running slope of a curb ramp, typically the gutter.
- Grade break: The line where two surface planes with different grades meet.
Perpendicular Curb Ramps (406.2)
| Element | Requirement |
|---|---|
| Landing (406.2.1) | 48 x 48 in. minimum at the top; may overlap pedestrian routes and clear spaces |
| Constrained landing | Where constrained at the back of sidewalk, 48 x 60 in., with the 60 in. in the direction of the curb ramp run |
| Landing slope | 1:48 maximum in all directions |
| Running slope (406.2.2) | Cuts through or is built up to the curb at right angles (or meets the gutter grade break at right angles on a curved curb); 1:20 minimum and 1:12 maximum |
| Run length | Not required to exceed 15 ft |
| Flared sides (406.2.3) | Where a pedestrian circulation path crosses the curb ramp, flared sides are required, sloped 10 percent maximum |
The 15-foot cap matters on steep streets: a curb ramp descending along a street with a steep grade may never reach 1:12 relative to level, so the code stops requiring additional length after 15 feet.
Parallel Curb Ramps (406.3)
| Element | Requirement |
|---|---|
| Landing (406.3.1) | 48 x 48 in. minimum at the bottom; may overlap pedestrian routes |
| Constrained landing | Where constrained on two or more sides, 48 x 60 in., with the 60 in. in the direction of the pedestrian street crossing |
| Landing slope | 1:48 maximum in all directions |
| Running slope (406.3.2) | In line with the direction of sidewalk travel; 1:20 minimum and 1:12 maximum; run not required to exceed 15 ft |
Parallel ramps suit narrow sidewalks: the sidewalk itself ramps down to a landing at street level.
Blended Transitions (406.4)
Running slope 1:20 maximum. Because a blended transition is not steeper than 1:20, it is not a ramp and does not need handrails, but it does need detectable warnings at street crossings.
Common Requirements (406.5)
| Section | Requirement |
|---|---|
| 406.5.1 Width | Curb ramp runs (excluding flared sides) and blended transitions 48 in. minimum |
| 406.5.2 Grade breaks | Perpendicular to the direction of the ramp run at the top and bottom; not permitted on the surface of ramp runs and landings; surfaces meeting at grade breaks are flush |
| 406.5.3 Cross slope | 1:48 maximum; at crossings without yield or stop control and at mid-block crossings, may equal the street grade |
| 406.5.4 Counter slope | Gutter or street at the foot of the ramp, blended transition or landing 1:20 maximum |
| 406.5.5 Clear space | Beyond the bottom grade break, 48 x 48 in. within the width of the crossing and wholly outside the parallel vehicle travel lane |
| 406.5.6 Marking | If adjacent curbs are painted, the paint extends along the flared portion |
| 406.5.7 Location | Curb ramps and flares may not project into vehicular traffic lanes, parking spaces or parking access aisles; at marked crossings, ramps are wholly within the markings (excluding flares) |
| 406.5.8 Obstructions | Located or protected to prevent obstruction by parked vehicles |
| 406.5.9 Handrails | Not required on curb ramps |
Detectable Warnings (406.6 and 705)
Section 406.6.1 says where detectable warnings are provided they comply with Section 705. Section 406.6.2 then requires them at:
- Curb ramps and blended transitions at pedestrian street crossings;
- Pedestrian refuge islands (except cut-through islands at street level less than 6 ft long in the direction of travel);
- Pedestrian at-grade rail crossings not within a street or highway;
- Boarding platforms at bus and rail transit stops where the platform edges are not protected by screens or guards;
- Boarding and alighting areas at sidewalk or street-level rail transit stops where the side facing the rail vehicles is not protected.
A117.1 Section 705 sets the dome geometry (base diameter, top diameter, height and spacing), visual contrast and the placement of the warning surface on each configuration; see Section 8.3 of this guide. IBC 1110.13 (2024; 1110.11 in 2021) scopes detectable warnings on passenger transit platform edges bordering a drop-off without screens or guards, and exempts bus stops.
Worked Example
A new campus street crossing uses perpendicular curb ramps. The sidewalk is 7 feet wide with a building face at the back.
- Ramp run: 48 inches wide minimum, running slope between 1:20 and 1:12. A 6-inch curb at 1:12 needs 72 inches of run.
- Top landing: 48 x 48 inches minimum, but because the landing is constrained by the building at the back of the sidewalk, 48 x 60 inches with 60 inches in the direction of the ramp.
- 72 inches of ramp plus 60 inches of landing is 132 inches, more than the 84-inch sidewalk. A parallel curb ramp or a blended transition is the practical solution.
- Detectable warnings are required because this is a pedestrian street crossing.
Exam Traps
| Trap | 2017 rule |
|---|---|
| 36-inch curb ramp width | 48 inches |
| 36-inch top landing | 48 x 48 inches (48 x 60 when constrained) |
| Flares 1:10 measured parallel to the curb, 1:12 with short landings | Flares 10 percent maximum where pedestrians cross the ramp |
| Handrails on curb ramps | Not required |
| Detectable warnings optional | Required at street crossings and the other 406.6.2 locations |
Under ICC A117.1-2017 Section 406.5.1, what is the minimum clear width of a curb ramp run, excluding flared sides?
36 inches
44 inches
48 inches
60 inches
A perpendicular curb ramp's top landing is constrained by a building at the back of the sidewalk. What landing size does A117.1-2017 require?
48 by 60 inches, with the 60-inch side along the curb ramp run
36 inches by 36 inches, matching the older ADA top landing size
48 inches by 48 inches, the same as an unconstrained top landing
60 inches by 60 inches
Which location does ICC A117.1-2017 Section 406.6.2 list as requiring detectable warning surfaces?
The top of every interior stairway
Every ramp landing on an accessible route
Curb ramps and blended transitions at pedestrian street crossings
Entrances to all toilet rooms
Sections you finish are checked off in the contents.