Subject : RE: Where roundabouts may be inappropriate
Here is a slide from a FHWA presentation on roundabouts about "Where may
roundabouts not be appropriate."
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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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