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speed bumps versus speed humps

 
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Subcity



Joined: 17 Mar 2010
Posts: 296

PostPosted: Mon Sep 27, 2010 6:03 pm    Post subject: speed bumps versus speed humps Reply with quote

Based on some research, it seems (i.e., I may be wrong about this) that "speed humps" are meant to slow traffic down to about 20 MPH or so, while "speed bumps" are intended to slow traffic to under 10 MPH. So, I wonder why there has been a proliferation of "speed bumps" on neighborhood streets - multiple bumps/block - where the speed limit is 25 MPH.

Apart from the impact on drivers in general, this is a significant matter for emergency response vehicles.

So, anyone know why it's bumps, not humps?

Footnote: To qualify my use of the word "wonder", I am not at all surprised that DDOT actually does this. Many of their initiatives seem to lack rigorous engineering/design. (And when I say "rigorous", I mean "any".) Even basic common sense can be hard to discern. So, perhaps I should say, I wonder if they know about the hump option.
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jack



Joined: 23 Mar 2004
Posts: 4762
Location: 19th & Lamont

PostPosted: Mon Sep 27, 2010 7:34 pm    Post subject: Re: speed bumps versus speed humps Reply with quote

Subcity wrote:
Based on some research, it seems (i.e., I may be wrong about this) that "speed humps" are meant to slow traffic down to about 20 MPH or so, while "speed bumps" are intended to slow traffic to under 10 MPH. So, I wonder why there has been a proliferation of "speed bumps" on neighborhood streets - multiple bumps/block - where the speed limit is 25 MPH.

Apart from the impact on drivers in general, this is a significant matter for emergency response vehicles.

So, anyone know why it's bumps, not humps?

Footnote: To qualify my use of the word "wonder", I am not at all surprised that DDOT actually does this. Many of their initiatives seem to lack rigorous engineering/design. (And when I say "rigorous", I mean "any".) Even basic common sense can be hard to discern. So, perhaps I should say, I wonder if they know about the hump option.


Those are humps, not bumps. The only speed bump I know of on streets around here is on Adams Mill Road going past Walter Pierce Park in Adams Morgan.

Humps vary in their aggressiveness. Those on Monroe Street, east and west of 16th, are fairly mild. Those on Newton, between 14th and 16th, are more severe. Is anybody at DDOT consciously designing these things? I'm skeptical.

Agreed that the consequences of speed humps on emergency vehicles is something people ought to think about. Do you really want to slow down those arriving fire engines, police cars, and ambulances?

That's why speed humps are not put on arterial routes, such as Park Road, Irving Street, and Adams Mill Road. (Adams Mill Road in Mount Pleasant is classified as an arterial, and residents along that road know how many emergency vehicles it sees. Adams Mill Road past the Irving intersection is no longer an arterial, so I guess that bump at Ontario is allowed.)

I'm told that the fire engines coming here for that attic fire on 19th Street last week got here in about four minutes, all the way from Georgia Avenue. No speed humps on that route, that's for sure.

-- Jack
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Subcity



Joined: 17 Mar 2010
Posts: 296

PostPosted: Mon Sep 27, 2010 8:32 pm    Post subject: Reply with quote

Jack, thanks for the comment. But, my reading of this document, "Guidelines for the Design and Application of Speed Humps", says what we have around here are mostly "speed bumps" - at least they require a lot less than 20 MPH. Not all of them, and not some of those on Monroe, but most. Certainly on Newton east of 16th, even 15 MPH would cause a problem. Call them what you will, we seem to agree on their impact being wrong according to apparent stanards. The doc is from the Institute of Transportation Engineers. Here's an image from that doc:
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jack



Joined: 23 Mar 2004
Posts: 4762
Location: 19th & Lamont

PostPosted: Mon Sep 27, 2010 9:08 pm    Post subject: Speed humps Reply with quote

I'm not a fan of speed humps of any sort. They're no fun on bicycles, either. But the residents who have demanded them, such as those on Monroe Street, and 17th, swear by them.

The key distinction between a "hump" and a "bump" is simply the length. Humps are supposed to be about 12 feet long, comparable to the distance between front wheels and rear. Bumps are quite short compared to the automobile wheelbase, and you've got to come to a near stop to go over those. (See that bump on Adams Mill Road, for example.)

That said, humps can be made so severe that they force very low speeds. In principle, the hump is designed to correspond to the desired allowable speed. In practice . . . I agree with your description of DDOT "engineering". I think hump design is just guesswork by the pavement contractor.

Re bumps:

There may be one exception to government discretion in the choice of traffic calming measures. One physical measure has been found by some courts to be patently unsafe when applied to public streets. It is the speed bump, as opposed to the longer speed hump. Speed bumps are abrupt features that rise and fall 3 to 4 inches over a span of 1 to 3 feet (see figure 6.6). Bumps have comfortable crossing speeds of 5 mph or less, which relegates them to parking lots and private driveways as opposed to public roadways with higher posted speed limits.

In Vicksburg v. Harrellton, a landmark case, the Mississippi Supreme Court ruled that speed bumps constituted an inherent danger to motorists. The Connecticut courts reached the same conclusion, but had another reason for declaring them a public nuisance: Their low design speeds could so delay emergency vehicles as to cause serious injury or loss of life. An occasional bump can still be found on a public roadway.

Traffic Calming: State of the Practice
ITE/FHWA, August 1999
Chapter 6: Legal Authority and Liability


-- Jack
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