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Inappropriate Places

Page history last edited by Frank Broen 13 years, 8 months ago

Subject : RE: Where roundabouts may be inappropriate

 

 Here is a slide from a FHWA presentation on roundabouts about "Where may

roundabouts not be appropriate."

 

[image: Screen shot 2010-07-10 at 10.12.57 AM.png]

 

One thing to notice is that unbalanced traffic is not mentioned here. I have

comments and questions about these:

 

*1. Unfavorable topography:* Why would a roundabout be worse than any other

intersection at steep grade? Not having to stop and restart on a steep grade

should be easier, especially with manual transmission. And what about

"beyond a crest vertical curve"? Is this because traffic lights would be

seen earlier over a crest than indications for a roundabout? If so,

couldn't advisory signage well before the roundabout provide sufficient

warning?

 

*2. Coordinated signal system*. Has this been modeled? Imagine three

coordinated signals A - B - C. Now we change B from a signalized

intersection to a roundabout. Will this actually increase delay through the

entire series of intersections compared to keeping B signalized?

 

*3. Periodic closures.* Hasn't this already been taken car of in some places

in Australia and in Nantes, France where trams cross in or near roundabouts?

 

*4. Reversible lane system.* I suppose this could be tough to handle on a

roundabout. Is this still done in some cities. I remember Tucson having some

of these on earlier visits there (a reversible lane, was it on Speedway?

that the called a "suicide lane." They seem to be all gone now. In contrast,

making a roundabout one-way seems easy--I see it often while watching the

Tour de France.

 

*5. Near a high traffic generator where manual intersection control is

frequent. *Can't a well designed roundabout handle occasional

higher-than-normal traffic, making manual control unnecessary? I have heard

that there are some roundabouts near large sports venues where there must be

higher traffic before and after games.

 

I would greatly appreciate comments about these claimed contra-indications

for roundabouts to see if they really have a firm basis in modeling,

research or practice, or are perhaps myths like the unbalanced load

contra-indication as indicated by Michael (mjwallwork).

 

-- Gary

--

Gary Cziko ("ZEE-ko")

Professor Emeritus, Educational Psychology, University of Illinois at

Urbana-Champaign

Vice-Chair, ChampaignCountyBikes.org

Member, Sustainability Advisory Commission, Urbana, IL

Member, Bicycle & Pedestrian Advisory Commission, Urbana, IL

Founder, TransitionChampaignCounty.org

 

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