Curb Extensions (AKA Sidewalk Bumpouts) 3

[cieg22]

Hello.
I'm working on a project that involves curb extensions aka sidewalk bumpouts at a busy intersection. The municipality wants us to drain the sidwalk extensions toward the street. However, the existing curb is about 4" high. With the roadway crowning upward and the sidewalk pitching downwarn, the reveal of the new curb would be miniscule. Does anyone know of a standard or guideline regarding mimimum allowable curb reveal from a safety standpoint? (The local DOT shows 8" on its standard details, but that is regularly disregarded.)

It just seems like a bad idea, and it would be extremely helpful to have a standard to back me up.

Thanks!

 

[bridgebuster]

Take a look at the NYCDOT Street Design Manual. There are a lot of photos; some might be of help.

http://www.nyc.gov/html/dot/html/about/streetdesignmanual.shtml

I don't do street design per se. However, it is a component on many of my projects. On NYC street projects all corners have pedestrain ramps, so there is no curb.

Could you install bollards as a safety measure?

 

[ACtrafficengr]

Show them the definition of barrier or vertically faced curb. I'd say a curb with less than 4" reveal cannot be considered barrier curb.

Check out Portland, OR's Greenstreet designs. They place rain gardens in curb extensions, reducing the load on their storm sewers, especially their combined sewer system.

You could use their approach to catch the sidewalk drainage and maintain the existing curb reveal.

http://www.portlandonline.com/BES/index.cfm?c=44407

"...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

 

[Debaser]

Does this build-out accomodate a pedestrian crossing, or could it be made to? That way you need zero upstand at the far edge (adjacent the traffic stream). Of course, profiling the surfacing of the build-out to maintain drainage to to carriageway could still prove tricky.

Given the usually small size of build-outs and the area to be drained, are they really so against you keeping the 4 inch/100mm upstand and draining either to a concrete channel block acting as a smooth conduit, the same way as the channel adjacent the kerb, or using some sort of open topped drainage channel, tying into and thereby maintaining the highway drainage run?

http://www.marshalls.com/select/PDF/Products/WMSD03.pdf

http://www.marshalls.com/select/PDF/Products/WMSD04.pdf

http://www.marshalls.com/select/PDF/Products/WMGS03.pdf

 

[TerryScan]

According to FHWA's Roadside Design Guide, curbs do not have a significant redirectional capability. It recommends that one attempt to maintain clear zones (vehicle recovery areas) as if there were no curb.

From the guide: "Curbs are commonly used for drainage control, pavement support and delineation, right-of-way reduction, aestheics, sidewalk separation, and reduction of maintenance operations."..."These are intended to discourage motorists from deliberately leaving the roadway"

In summary, curbs are not a vehicle barrier.

 

[civilman72]

To clarify the post above, vertical curb is not considered a traffic barrier for high-speed roadways, but is considered a barrier for roads with speeds less than 35 mph.

So, if this curb is intended to serve as a traffic barrier, then maintaining the reveal between the vertical curb and driving surface is important. 6” of vertical curb would be desirable, but considering the existing curb is 4” you can probably argue that this should be you minimum height.

If this curb is not intended to be a vehicle barrier, then I do not see a reason you need to maintain the existing reveal.

 

[TerryScan]

To further clarify-

Vertical curb is considered a hazzard above 35mph (due to potential of a vehicle launching or overturning). This does not mean it a barrier at lower speeds. It is a traversable obstacle below 35mph and, as quoted above, is intended to discourage motorists from leaving the roadway.

I did have an 8-12" vertical curb stop my vehicle when I lost control on an icy bridge and struck the curb perpendicularly with both front tires (from a spin).

Otherwise, I am rather confident that at 5mph, I will mount a 6" curb if I strike it at most angles with my vehicle. It may deflect the vehicle's path dependant upon many variables.

 

[ACtrafficengr]

It's more of a psychological barrier than a physical barrier, which is why it is now called vertical faced curb I should have put "barrier" in quotes.

On the other hand, a recent study out of Connecticut found curbed sidewalks are associated with a 7 mph reduction in median speeds. The only other things they found that had an influence were building setback and on-street parking.

"...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

 

[Debaser]

"According to FHWA's Roadside Design Guide, curbs do not have a significant redirectional capability. It recommends that one attempt to maintain clear zones (vehicle recovery areas) as if there were no curb.

From the guide: "Curbs are commonly used for drainage control, pavement support and delineation, right-of-way reduction, aestheics, sidewalk separation, and reduction of maintenance operations."..."These are intended to discourage motorists from deliberately leaving the roadway"

In summary, curbs are not a vehicle barrier."

Do you use these kerbs on that side of the Atlantic? Not a barrier as such, but useful for keeping Heavy Goods Vehicles and the like on track for most striking angles less than say 75-90 degrees.

http://www.brett.co.uk/images/Trief_Kerb.pdf

 

[ACtrafficengr]

Debaser, I've never seen that before. How effective are they? How much do they cost per meter?

"...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

 

[Debaser]

@ACtrafficengr

See also this pdf for more details re dimensions (different manufacturer, same idea, the original product being the Trief above).

http://www.marshalls.co.uk/select/PDF/Products/KERB01.pdf

http://www.marshalls.co.uk/select/s...material=&product=Titan+Kerb&type=Photography

It was designed purposely to redirect large vehicles (Heavy Goods Vehicles and buses) travelling more or less parallel to the direction of laying. Having said that, its height will stop most of the vehicles that use our roads from transgressing, the exception being large tipper wagons as used in quarries, etc., with large diameter tyres.

In the past I've specified it on either side of a semi-permanent bridge that was going to carry a percentage of HGVs, as a belt and braces measure together with normal safety barrier. This stuff was put down to prevent all but the most determined drivers coming into contact with the barrier.

The design is such that lorry tyres will ride up the slope, before the bulge at the top of the kerb redirects the wheel without damage. I have seen photos of this specific interaction but can't find them at present.

Do a Google search on 'containment kerb' (with or without adding 'UK') or 'Trief kerb' to get some better examples.

I'll try and look up a cost and post back.