Measuring/Designing Curb Ramp Slopes

[jkellerfsu]

I have been working over the past few years developing ADA standards within the right-of-way. I am curious to get a feel for how anyone (IF ANYONE) interprets the 12:1 runnng slope for a pedestrian curb ramp. MD SHA and The City of Baltimore have interpreted "12:1 requirement" to mean "a change in elevation over distance".

Given that we are constricted within limited ROW (especially in urban areas) we do not interpret 12:1 to necessarily absolutely equal 8.33% (don't gasp!), our curb ramp length is governed by the height of the curb (6" curb yeilds a 6' ramp)

The access board seems to be favoring our interpretation. Does anyone else have the same feeling? I have recently dealt with a "Department of Justice certified Architect" who verifies compliant ramps all over the country - not one municipality has proposed this argument.

 

[civilperson]

What is the question? All your examples fit the parameters of 8.33% or 1 inch rise in 12 inch run or 6" curb in 6 foot ramp. This standard is held in all the municipalities that I have dealt with even to the extent of requiring a hairpin curve and double ramp for a natural grade of 15%.

 

[CarlB]

Do you mean your ramp length is 6' (ties into sidewalk/other grade 6' away horizontally) but that the elevation from beginning to end of ramp may be more than 6"? I haven't seen a specific reference to this case, but I've interpreted the requirement to be an actual slope no greater than 8.33%. I've noticed several designs and installations that didn't account for the roadway grade resulting in steeper than 1:12 ramps, I've attributed it to lack of care by designers/reviewers/contractors.

 

[jkellerfsu]

This is an excerpt from a memo penned here at the city:

ADA Standards for Accessible Design 28 CFR part 36 Sections 4.1.6 and 4.7 require running and flare slopes of 1:10 in existing facilities and 1:12 in new construction. Transitions from ramps to walks, gutters, or streets shall be flush and free of abrupt changes. Maximum slopes of adjoining gutters, road surface immediately adjacent to the curb ramp, or accessible route shall not exceed 1:20.

The ramp slope is a ratio equal to the vertical rise divided by the horizontal run (x). It is equal to the tangent of the angle that the plane of the ramp surface makes with a horizontal (level) plane. Thus, a .5’ curb yields a 6.0’ curb ramp length.

.5’ curb: 6.0’ ramp length = .083 or 1:12

Merely placing a digital level on the running slope will yield erroneous results at any location where roadway slope ? 0. The ramp and flare lengths are dependent on curb height since we are measuring a change in height over distance (x). By measuring a slope with a digital level we constrain the design requirements unnecessarily. The classic example to demonstrate the argument is on a roadway with an 8.3% slope. It is mathematically impossible to design a ramp with an 8.3% slope (as measured with a digital level) but not impossible to design a ramp that changes .5’ height over 6.0’. Using the latter methodology allows the DOT to be compliant attaining a 1:12 slope.

This method does take in account the surrounding terrain - in fact it relies on it.

I have many diagrams but I don't know how to attach them on this forum.

 

[GeoPaveTraffic]

The requirements have always seemed very clear to me. The ramp cannot have a slope greater than a 1" rise in 12". If the ground grade is rising, then you have to add walls, etc. to limit the grade change in the ramp. You also have to have a landing zone at the top of the ramp with a maximum slope of 2% in any direction.

If you have limited right-of-way there a differing ramp designs that will allow you to meet the ADA requirements.

 

[ACtrafficengr]

As the grade of the sidewalk increases, it becomes infeasible to provide a 1 on 12 ramp. NYSDOT guidance is:

Curb ramps should be constructed with the running slope no flatter than 5% and the maximum traversable slope in the direction of pedestrian travel not to exceed 8.33%.
However, in situations where the roadway itself exceeds 8.33%, the length of a parallel curb ramp does not have to exceed 4.5 m. The project designer may choose to continue the ramp at an 8.33% slope beyond the 4.5 m, or opt for a slope greater than 8.33% after the 4.5 m.

http://www.dot.state.ny.us/cmb/consult/hdmfiles/chapt_18.pdf,

Section 18.7.3.

On a steep slope, a level landing before entering the roadway will help wheelchair users going downhill stop before entering the intersection. I know it complicates design, but it is worth thinking about.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[ACtrafficengr]

Another link worth looking at:

http://www.access-board.gov/prowac/

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[jkellerfsu]

PROWAC is in the draft phase and is addressing this very issue in the final. I think many engineers/designers do not realize it's a draft. I just recently learned this myself within the past few months by communications with the access board itself.

In Baltimore, we have a variable terrain with many steep grades. Our sidewalks are typically no wider than 14 feet (usually less) with building faces at the ROW line. How do you deal with that situation? 4.5 m tie-in just doesn't cut it.

 

[ACtrafficengr]

While it's true that the PROW regs haven't been adopted, parts of the ADAAG apply to sidewalks.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[jkellerfsu]

Of course ADAAG applies to sidewalks but it was developed with vertical structures on level surfaces in mind - that's how PROWAC came to be.

I am not trying to convince anyone to join my battle, just want to know who is really dealing with this in an urban setting.

I deal equally with State DOT and the City. The state was the originator of the concept and has a lot more ROW to use - here in the City, aquiring ROW is just not possible.

 

[GeoPaveTraffic]

jkellerfsu

The way you deal with limited right-of-way is to change the way you build the ramp. It is difficult to explain, but here goes.

Starting at the curb, instead of going up to meet the sidewalk in a radius, put a landing. Then take two ramps up, one to meet each of the approaching sidewalks.

 

[jkellerfsu]

Geopavetraffic

I think I know what you are explaining. What I envision you explain however will expose building foundations OR not provide the minimum "passing" space for peds at the ramps.

I may be thinking the wrong thing though. I am probing for that breakthrough idea lol.

Using your idea- how would you design that on a corner (low point on radius) with intersecting profiles, say 10%? This is a common occurence downtown.

 

[ACtrafficengr]

Could you convert a plan sheet to jpg and post it on Photobucket or a similar site? I know AutoCAD '04 will do that. Maybe if we could see your problem, we could give you better suggestions.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[jkellerfsu]

 

[jkellerfsu]

 

[GeoPaveTraffic]

jkellerfsu,

I'll take a look at the pictures and get back to you over the weekend. Our Firewall will not let me view the photos from work.

 

[civilman72]

Working in the Rocky Mountains in Colorado, I have dealt with attempting to add sidewalks and curb ramps to existing roads that are steep (6%-9%). As previously discussed and based on my experience, attempting to add curb ramps that are under ADA max. grade requirements is nearly impossible to do if attaching to road grades over say 5%. The only way to truly meet the 12:1 max grade is to design ramps that can be up to 50' to 100' long - as depicted in the sketches on the post from jkeller.

One thing I have also struggled with, that I do not believe has been mentioned yet, is that any ADA access over 5% requires a handrail (not necessary for short ramps), and a "flat" areas every 30'(approximately). When attaching to an existing road with steep grades, attempting to meet these two requirements can be unsightly, expensive, and simply impractical.

About five years ago, as a part of the civil design for a new bank, I was given the task of designing a sidewalk (to ADA standards) adjacent to an existing steep road. The sidewalk used to access the site internally would tee-off from the proposed sidewalk adjacent to this existing road.

My boss at the time informed me of a very helpful group from Colorado Springs that helped individuals like ourselves with ADA Standards and how to apply them to our site designs. I found this group VERY helpful, at least five years ago, so here's a link if you are interested:

http://www.adainformation.org

In a nutshell, what they told me was to make sure that within the new site, I did everything I could to meet the ADA requirements. But when connecting to existing infrastructure, the proposed sidewalks and ramps should be designed to best-fit into the existing infrastructure. So for my example, we attached the sidewalk to the existing road (around 9% ex. grade), and did not include flat areas or handrails. But once the sidewalk entered the private, undeveloped land, we designed all ramps and grades to meet ADA Standards.

This solution may be too simplistic (and based on one's interpretation of the ADA regulations) but it is an interpretation that I have not yet seen mentioned, so I thought it was worth throwing out there.