Problems with curb ramps and little girl photo bombs.

July 9, 2010

The problem with a perpendicular curb ramp is that it will often take up most of your sidewalk; see my post on Why Your Curb Ramp is too Steep for more on that.

The minimum width of an accessible route is 36″ and since the accessible route cannot have a cross slope greater than 2%, the route must go around a curb ramp rather than across a curb ramp.  In the first photo, we have a perpendicular curb ramp that occupies most of the sidewalk, but as long as the clearance from the top of the curb ramp to the facade is 36″ or more, it is acceptable.

Little Girl Photo Bomb!

In this second photo, the clearance between the column and the top of the ramp is less than 36″ and the accessible route has been disrupted.  This curb ramp and the accessible parking it serves should be relocated or reconfigured so that the accessible route is maintained across the front of the shopping center.

It is also important to keep perpendicular curb ramps out of the maneuvering clearance required at doors.


Contrasting Curb Ramps and Detectable Warnings

May 13, 2009

To quote the TDLR Technical Memorandum 08-01, “With the intention of harmonizing both State and Federal requirements, the Department issues the following technical clarifications regarding surface texture requirements at curb ramps.”

TM 08-01 then goes on to confuse the issue further by treating differently curb ramps within the public ROW (right of way) and those that are not within the ROW.

From the Texas Accessibility Standards (italics denote a change from the ADAAG):

4.7.4 Surface. Surfaces of curb ramps shall comply with 4.5.

(1) Textures shall consist of exposed crushed stone aggregate, roughened concrete, rubber, raised abrasive strips, or grooves extending the full width and depth of the curb ramp. Surfaces that are raised, etched, or grooved in a way that would allow water to accumulate are prohibited.

(2) For purposes of warning, the full width and depth of curb ramps shall have a light reflective value and texture that significantly contrasts with that of adjoining pedestrian routes.

Contrasting curb ramp on private property.

Contrasting curb ramp on private property.

Per TM 08-01, section 4.7.4(1) & (2) do not apply to curb ramps within the public ROW.  Instead, these curb ramps shall have detectable warnings that comply with section 4.29.2:

4.29.2* Detectable Warnings on Walking Surfaces. Detectable warnings shall consist of raised truncated domes with a diameter of nominal 0.9 in (23 mm), a height of nominal 0.2 in (5 mm) and a center-to-center spacing of nominal 2.35 in (60 mm) and shall contrast visually with adjoining surfaces, either light-on-dark, or dark-on-light.

The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact.

The ADAAG(1991) and the revised ADA/ABA Guidelines(2004), do not specify contrast for curb ramps.  The contrast is a requirement for the detectable warnings which are required to be provided on curb ramps.

There is no conflict for curb ramps within the ROW; the contrast is only required on the detectable warnings.  The remainder of the curb ramp may be plain concrete.

If a curb ramp is not located within the ROW, section 4.7.4(2) still applies; the full width and depth of the curb ramp shall contrast with adjoining pedestrian routes even if detectable warnings are not used.

Don’t try too hard to understand it.  This story is not over.


It’s not a Flat Earth: Why your curb ramp is too steep.

April 7, 2009

It happens all the time on inspections.  I’m standing in the August heat trying to explain to a contractor or architect why the 6 foot long curb ramp is too steep.

They argue that since the curb is 6 inches high, the ramp need only be 6 foot long to achieve the 1:12 (8.3%) slope permitted by the ADA.  The fact that my electronic level reads a slope of 10.4% is usually ignored in a fit of cognitive dissonance.

So how can it be that a 6 foot long ramp is insufficient for a 6″ curb? 1″ in 12″, right? Nope, because you aren’t trying to get to the top of the curb.  Take a look at this diagram:

curb-ramp-diagram

Most sidewalks running along buildings (strip shopping centers are a good example) have a slope of 1/4″ per foot to allow for drainage away from the building.  This slope is usually continuous to the curb.  The curb ramp is fighting this 1/4″ per foot rise as it cuts into the sidewalk; for every foot of ramp length, the height increases by 1/4″.  In the example above a 6′ ramp will have a running slope of 10.4% (7-1/2″ rise with a 72″ run).

To comply with the ADAAG, the curb ramp must be 8 foot long to achieve a maximum running slope of 8.3%.  And, no, handrails are not required on curb ramps regardless of the length.

If 8′-0″ is too long, try using a parallel curb ramp that slopes parallel to the curb and doesn’t have to fight the incline.