Roundabouts as interstate exits?

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Larry Gross

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Oct 17, 2005, 6:27:01 AM10/17/05
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I-485 roundabouts to keep traffic moving

If roundabouts are your thing, you'll get a chance to circle them at
three future interchanges on Interstate 485.

Admittedly these one-lane roundabouts will take some getting used to,
but I think drivers will come to appreciate how they keep traffic
moving.

Roundabouts, what few we have, are usually found on less-traveled roads
where they eliminate the need for traffic signals and reduce
collisions.

The state is building a roundabout on each side of three outerbelt
exits to avoid installing ramp traffic signals, usually a serious
choke-point for traffic.

http://www.charlotte.com/mld/observer/12915680.htm

does anyone have a pix or graphic of one of these critters?
are these interchange ramps SPUIs?

Mr Sparkle

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Oct 17, 2005, 8:02:18 AM10/17/05
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Adam Prince

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Oct 17, 2005, 9:00:23 AM10/17/05
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They aren't SPUI's. We toured one of the ones last October at the
Charlotte Meet. I do not have any photos of them...but if anyone at
that meet did, send them out and I can throw a quick update together
for them.

--Adam

Bob S

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Oct 17, 2005, 9:28:03 AM10/17/05
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Larry Gross wrote:
> I-485 roundabouts to keep traffic moving
>
> If roundabouts are your thing, you'll get a chance to circle them at
> three future interchanges on Interstate 485.
>
> Admittedly these one-lane roundabouts will take some getting used to,
> but I think drivers will come to appreciate how they keep traffic
> moving.
>
> Roundabouts, what few we have, are usually found on less-traveled roads
> where they eliminate the need for traffic signals and reduce
> collisions.
>
> The state is building a roundabout on each side of three outerbelt
> exits to avoid installing ramp traffic signals, usually a serious
> choke-point for traffic.

WisDOT & the City of Madison installed a roundabout at the Thompson Dr.
exit off of eastbound WI 30 (a freeway spur into Madison from
I-39/90/94). The roundabout is at the ramp intersection with Thompson
Dr. which feeds into another roundabout at Commercial Ave. So what you
have is back-to-back roundabouts. I would have to say that the
roundabouts have improved traffic flow through the area considerably.
There were big backups when the Thompson Dr/Commercial Ave intersection
was a 4-way stop, which caused traffic to backup on the exit ramp.

Bob S

Michael G. Koerner

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Oct 17, 2005, 10:54:59 AM10/17/05
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What about that roundabout at that new Beltline (US 12) interchange in Middleton?

Also, WisDOT is planning roundabouts at the US 41/WI 55 interchange
intersections in Kaukauna (mentioned in another posting that I made last week).

There have been roundabouts at an I-70 interchange in Vail, CO for many years
now, too.

--
___________________________________________ ____ _______________
Regards, | |\ ____
| | | | |\
Michael G. Koerner May they | | | | | | rise again!
Appleton, Wisconsin USA | | | | | |
___________________________________________ | | | | | | _______________

Garrett Wollman

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Oct 17, 2005, 12:05:54 PM10/17/05
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In article <kKqdnRC7-e7ZJs7e...@athenet.net>,

Michael G. Koerner <mgk...@dataex.com> wrote:
>There have been roundabouts at an I-70 interchange in Vail, CO for many years
>now, too.

And of course, traditional rotary interchanges (similar to those
common in Britain) have been a staple of Massachusetts highway design
for the better part of a century. Some examples:

I-91: SR 2/2A (Greenfield)
I-93: SR 28 (Roosevelt Circle)
I-95: US 1 (Foxboro/Sharon), US 1 (Topsfield), US 20 (Waltham)
US 6: Mid-Cape Highway termini
SR 9: Speen St. (Natick) (signalized, with bypass ramps)
SR 25: Bourne end of the Bourne Bridge

Some of them work better than others.

-GAWollman

--
Garrett A. Wollman | As the Constitution endures, persons in every
wol...@csail.mit.edu | generation can invoke its principles in their own
Opinions not those | search for greater freedom.
of MIT or CSAIL. | - A. Kennedy, Lawrence v. Texas, 539 U.S. 558 (2003)

Robert Cruickshank

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Oct 17, 2005, 12:12:12 PM10/17/05
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Larry Gross wrote:
> does anyone have a pix or graphic of one of these critters?
> are these interchange ramps SPUIs?

Below is a link to a Google maps satellite image of I-17 at Happy Valley
Road, just north of Phoenix. The exits/entrances to I-17 are roundabouts.

http://tinyurl.com/c4fkb

--
Robert I. Cruickshank
roadgeek, historian, progressive

stev...@pressenter.com

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Oct 17, 2005, 12:38:40 PM10/17/05
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Michael G. Koerner wrote:
>
> What about that roundabout at that new Beltline (US 12) interchange in Middleton?
>
> Also, WisDOT is planning roundabouts at the US 41/WI 55 interchange
> intersections in Kaukauna (mentioned in another posting that I made last week).
>
> There have been roundabouts at an I-70 interchange in Vail, CO for many years
> now, too.
>

They are very nearly finished with a new one of these at the
intersection of WI-35 and Hanley Road in Hudson, just south of the I-94
interchange. Mind you, they've been _nearly_ finished with it for
about two months now... I don't understand why they've waited this long
to put the finishing touches on it.

Steve Manfred
River Falls, WI

argatla...@yahoo.com.mx

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Oct 17, 2005, 12:40:44 PM10/17/05
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[Mr. Cruickshank:]

> Below is a link to a Google maps satellite image of I-17 at Happy Valley
> Road, just north of Phoenix. The exits/entrances to I-17 are roundabouts.
>
> http://tinyurl.com/c4fkb

The Arizona Transportation Research Center has a report (S.P.R. 545) on
the Happy Valley roundabouts, which were installed as an interim
improvement and are intended to stay in place until funding is
available to widen the bridge over I-17 and expand the interchange
(probably to a S.P.U.I.). The table of contents *.PDF can be accessed
here:

http://www.azdot.gov/TPD/ATRC/publications/project_reports/PDF/AZ545/AZ545_index.pdf

The Happy Valley roundabouts, which were the first on the Arizona state
highway system, were not an unqualified success. They were widely
resented at first, because (1) members of the public assumed (wrongly)
that they were meant to replace a more competent improvement such as
the planned S.P.U.I., and (2) the initial design was unrefined, which
resulted in a higher-than-expected number of accidents and forced
Arizona D.O.T. to come back and tinker with the design.

Although roundabouts are now being used on locally maintained roads in
Arizona, bad feelings about the Happy Valley roundabouts still persist.
In the last legislative session, these resulted in a bill (S.B. 1222)
being introduced which would have required a petition (signed by 51% of
voters living within five miles of the proposed roundabout) or a local
government resolution before a roundabout could be constructed.

http://www.azleg.state.az.us/FormatDocument.asp?inDoc=/legtext/47leg/1r/bills/sb1222p%2Ehtm&DocType=B

Although the bill does not appear to have passed and is, indeed, both
silly and bad policy, it appears that Arizona D.O.T. did not do as well
as it might have in explaining its position.

http://www.azleg.state.az.us/FormatDocument.asp?inDoc=/legtext/47leg/1R/comm_min/House/030305TRANS.DOC.htm

In pertinent part:

[begin quote]

Mr. Prezelski said he believes ADOT already has a public input process
and asked if this bill was created for a specific situation where the
system failed, or is this about an institutional breakdown where we
have to change the law for one specific situation. Senator Martin
responded that when he met with ADOT about the roundabout, they blew
him off, and basically told him roundabouts are what we like, that is
what we will construct, you cannot tell us otherwise, and there is
nothing you can do about it. ADOT responded in kind to the city
council, the county supervisor, and to everyone who contacted ADOT
regarding the roundabout. ADOT did not consider it necessary to
solicit comments from local residents for intersection off-ramps
projects.

[end quote]

brink

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Oct 17, 2005, 1:38:10 PM10/17/05
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<argatla...@yahoo.com.mx> wrote in message
news:1129567244....@o13g2000cwo.googlegroups.com...

> [Mr. Cruickshank:]
>
>> Below is a link to a Google maps satellite image of I-17 at Happy Valley
>> Road, just north of Phoenix. The exits/entrances to I-17 are roundabouts.
>>
>> http://tinyurl.com/c4fkb
>
> The Arizona Transportation Research Center has a report (S.P.R. 545) on
> the Happy Valley roundabouts, which were installed as an interim
> improvement and are intended to stay in place until funding is
> available to widen the bridge over I-17 and expand the interchange
> (probably to a S.P.U.I.). The table of contents *.PDF can be accessed
> here:
>
> http://www.azdot.gov/TPD/ATRC/publications/project_reports/PDF/AZ545/AZ545_index.pdf
>
> The Happy Valley roundabouts, which were the first on the Arizona state
> highway system, were not an unqualified success. They were widely
> resented at first, because (1) members of the public assumed (wrongly)
> that they were meant to replace a more competent improvement such as
> the planned S.P.U.I., and (2) the initial design was unrefined, which
> resulted in a higher-than-expected number of accidents and forced
> Arizona D.O.T. to come back and tinker with the design.
>
> Although roundabouts are now being used on locally maintained roads in
> Arizona, bad feelings about the Happy Valley roundabouts still persist.
> In the last legislative session, these resulted in a bill (S.B. 1222)
> being introduced which would have required a petition (signed by 51% of
> voters living within five miles of the proposed roundabout) or a local
> government resolution before a roundabout could be constructed.

dang, all this hubbub over a *roundabout*? am i missing something here?
was this really a poorly engineered interchange or is this what i think it
is, good old fashioned unadaptable-don't-make-me-think-while-driving
whining?

brink


brink

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Oct 17, 2005, 1:54:35 PM10/17/05
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"Larry Gross" <gross...@gmail.com> wrote in message
news:1129544821.6...@g49g2000cwa.googlegroups.com...

here's a nice shot of a roundabout exit as it was nearing completion in
north topeka, KS on US 75 at the 46th street interchange:

http://maps.google.com/maps?q=topeka,+KS&ll=39.129161,-95.719199&spn=0.003993,0.012883&t=k&hl=en

this interchange is now completed and i believe US 75 is interstate standard
all the way from carbondale, KS (about 10 miles south of topeka) to about a
mile or so north of the 46th street interchange pictured here.

back when this was an at-grade intersection, this was an infamous spot for
horrible accidents. there was only a stop sign for traffic wishing to cross
or enter from 46th street and big trucks would come barrelling down the hill
from the north and plow into unwary drivers. over the years, this was
upgraded to a signaled intersection, which helped, but didn't eliminate the
fatal accidents.

i'm guessing the new grade separation/roundabout tandem has eliminated
fatalities here.

topeka has gone fairly roundabout crazy by the way... last time i was there
(may) i counted four new roundabouts... the big one discussed above plus
several other large ones on major surface arterial streets in west topeka...

brink


fro...@mississippi.net

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Oct 17, 2005, 5:12:12 PM10/17/05
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> stev...@pressenter.com wrote:
>
> They are very nearly finished with a new one of these at the
> intersection of WI-35 and Hanley Road in Hudson, just south of the I-94
> interchange. Mind you, they've been _nearly_ finished with it for
> about two months now... I don't understand why they've waited this long
> to put the finishing touches on it.

I recall reading an article on this one lately. Is there an
interchange on WI 35 at Hanley, with the roundabouts at the ramp
termini? Or is it an at-grade intersection between WI 35 and Hanely
with it now being a roundabout? The article wasn't clear on which was
the case.

Froggie | Picayune, MS | http://www.ajfroggie.com/roads/

fro...@mississippi.net

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Oct 17, 2005, 5:13:16 PM10/17/05
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> Adam Prince wrote:
>
> They aren't SPUI's. We toured one of the ones last October at the
> Charlotte Meet. I do not have any photos of them...but if anyone at
> that meet did, send them out and I can throw a quick update together
> for them.

I have photos, but they're in my perpetual backlog...

argatla...@yahoo.com.mx

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Oct 17, 2005, 6:25:48 PM10/17/05
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['brink':]

> dang, all this hubbub over a *roundabout*? am i missing something here?
> was this really a poorly engineered interchange or is this what i think it
> is, good old fashioned unadaptable-don't-make-me-think-while-driving
> whining?

Actually, it is a little of both. S.P.R. 545 goes into some of the
background. Prior to the roundabouts, stop sign control was used at
the ramp termini. But a business park was set to open nearby and
funding for the S.P.U.I., which was planned as part of a future
widening of I-17, was nowhere on the horizon. Roundabouts were the
logical answer since the geometry of the interchange (two-way frontage
roads intersect Happy Valley Road near the ramp termini) made it
difficult to provide a temporary signal installation.

There is abundant reason for believing that the roundabouts have saved
much more in terms of accidents and personal injury than simply leaving
the stop signs would have, but the initial design was not optimum.
This seems to have created a public perception that the state D.O.T.
wanted to force a novel intersection type it did not even know how to
design correctly down the throats of unwilling motorists.

I don't know what advance publicity Arizona D.O.T. did for the Happy
Valley roundabouts. There is an Arizona roundabouts site at

http://www.azdot.gov/CCPartnerships/Roundabouts/faq.asp

but it could very well be an example of closing the barn door after the
horse bolted.

I don't know how much weight to assign to the state senator's claim
that Arizona D.O.T. told him they didn't need to consult about off-ramp
improvements. While this may be true--every state D.O.T. has to draw
the line somewhere between soliciting public opinion and simply
carrying on with its construction and design activities--public
consultation would probably have been a good idea here. It could have
been justified as a special case since the proposed intersection design
was new to Arizona. However, I don't know if the D.O.T. would have had
enough time to take a reading of public opinion and still get the
roundabouts designed and built before the business park started adding
large amounts of traffic to that part of the network.

On the other hand, there have been the usual reports of people taking
lengthy detours to avoid going through the roundabout, which often
indicates conscious refusal to adapt to or accept a novel traffic
arrangement.

P.S. I am from Kansas originally, so I know some of the Kansas
roundabouts fairly well. The locally built ones in Topeka and Wichita
are just about perfect, as is the K-68 roundabout near Paola. However,
the interchange roundabouts on I-135 in Newton are far too eccentric in
shape to permit smooth comfortable circulation, and the ones in
Manhattan have excessive adverse camber in the circulatory carriageway.
I don't know enough about the local ones in Lawrence or the U.S. 75
interchanges north of Topeka to have an opinion on them.

John Lansford

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Oct 17, 2005, 6:30:52 PM10/17/05
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"Larry Gross" <gross...@gmail.com> wrote:

The ones I'm familiar with where roundabouts are at interchanges, the
ramps are simple ramps at diamond interchanges and there are two
roundabouts (one on each side of the bridge). They work very well to
keep traffic moving once the unfamiliarity is overcome by the
motorists.

John Lansford, PE
--
The unofficial I-26 Construction Webpage:
http://users.vnet.net/lansford/a10/

Scott M. Kozel

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Oct 17, 2005, 6:34:52 PM10/17/05
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"Mr Sparkle" <dfi...@earthlink.net> wrote:

>
> Larry Gross wrote:
>
> > does anyone have a pix or graphic of one of these critters?
> > are these interchange ramps SPUIs?
>
> Check out http://www.i75millcreekexpressway.com/alternatives.htm
>
> http://www.i75millcreekexpressway.com/images/pdfs/PDF%20Aternatives/PAD_B.pdf

This MDOT SHA news release announced the completion of a new Interstate
interchange that has roundabouts between the ramp terminals and the
local road:

"Good News for Prince George’s County Residents and Commuters"
http://www.sha.state.md.us/information/newsrel/oc/newstxt.asp?filename=03_07_14.27.z

"(July 14, 2003) -- The Maryland Department of Transportation’s State
Highway Administration (SHA) will open a new interchange along
I-95/I-495 (Capital Beltway) at Ritchie Marlboro Road in Prince George’s
County on Tuesday, July 15 at approximately 10 a.m. The new
interchange, which will be exit 13 along I-95, is located between exit
15, MD 214 (Central Avenue) and exit 11, MD 4 (Pennsylvania Avenue)".

"The new interchange features new ramps, a diamond interchange with
roundabouts at the bottom of the ramps and a new eight-foot sidewalk and
bicycle path along eastbound Ritchie Marlboro Road. Motorists exiting
either north or southbound I-95 onto the new Ritchie Marlboro Road exit
will enter a roundabout to access the proper destination.

Here is a 2002 Terraserver image, and it shows the new interchange under
construction --
http://tinyurl.com/awkdj

--
Scott M. Kozel Highway and Transportation History Websites
Virginia/Maryland/Washington, D.C. http://www.roadstothefuture.com
Philadelphia and Delaware Valley http://www.pennways.com

jdunlop

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Oct 17, 2005, 6:58:07 PM10/17/05
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I have some pictures at the office that I took in January, and
eventually they'll go on the web, on our roundabout web page (don't
bother looking for it right now, it doesn't exist yet, it's a
relatively low priority.) If you're interested, I have pictures of
most of the roundabouts in the state.

Anyway, I believe the one at Prosperity Church Road will have six
roundabouts, three on either side of the interstate at each crossroad.
Must simpler than the plan to combine some of the side roads, and works
better than signalizing the intersections.

rickmastfan67

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Oct 17, 2005, 7:13:23 PM10/17/05
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I know of a roundabout as an exit that isn't on an interstate. It's at
NY-5 and NY-179 just outside of Buffalo.

Michael G. Koerner

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Oct 17, 2005, 7:33:41 PM10/17/05
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I believe that WI 35 is being upgraded to interstate compatibility there and
this is for a new diamond interchange. On the maps, it looks like a likely
place for such an interchange.

I'm still a bit amazed that that is actually inside of the City of Hudson.

Wow.

pigst...@yahoo.com

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Oct 17, 2005, 10:25:54 PM10/17/05
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>
> On the other hand, there have been the usual reports of people taking
> lengthy detours to avoid going through the roundabout, which often
> indicates conscious refusal to adapt to or accept a novel traffic
> arrangement.
>
> P.S. I am from Kansas originally, so I know some of the Kansas
> roundabouts fairly well. The locally built ones in Topeka and Wichita
> are just about perfect, as is the K-68 roundabout near Paola. However,
> the interchange roundabouts on I-135 in Newton are far too eccentric in
> shape to permit smooth comfortable circulation, and the ones in
> Manhattan have excessive adverse camber in the circulatory carriageway.
> I don't know enough about the local ones in Lawrence or the U.S. 75
> interchanges north of Topeka to have an opinion on them.

I made the mistake of getting off I-70 eb at the one that is under
contruction at Rifle. I sat on the ramp for a long time, waiting for
traffic to clear so I could enter the roundabout. It reminded me of
the old traffic circles in NJ.
But at least there they put in traffic signals to provide breaks in
traffic.

It seems to me this one is too small to handle heavy volumes of traffic.

Dan Vincent

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Oct 17, 2005, 11:01:07 PM10/17/05
to
>I know of a roundabout as an exit that isn't on an interstate. It's at
>NY-5 and NY-179 just outside of Buffalo.

Tons of em over here on US/MA routes in MA, but there is an actual
traffic circle interchange with an interstate, with MA 2/2A/I-91 in
Greenfield, MA.

The more troublesome of these, like the Bourne/Sagamore rotaries are
being replaced with flyover ramps. They cause too many accidents when
the traffic counts get too high because they weren't designed for
incredbily high traffic counts nor moron drivers who don't yield for
traffic in the rotary.

Steve

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Oct 17, 2005, 11:15:54 PM10/17/05
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pigst...@yahoo.com wrote:

>>On the other hand, there have been the usual reports of people taking
>>lengthy detours to avoid going through the roundabout, which often
>>indicates conscious refusal to adapt to or accept a novel traffic
>>arrangement.
>>
>>P.S. I am from Kansas originally, so I know some of the Kansas
>>roundabouts fairly well. The locally built ones in Topeka and Wichita
>>are just about perfect, as is the K-68 roundabout near Paola. However,
>>the interchange roundabouts on I-135 in Newton are far too eccentric in
>>shape to permit smooth comfortable circulation, and the ones in
>>Manhattan have excessive adverse camber in the circulatory carriageway.
>> I don't know enough about the local ones in Lawrence or the U.S. 75
>>interchanges north of Topeka to have an opinion on them.
>
>
>
>
> I made the mistake of getting off I-70 eb at the one that is under
> contruction at Rifle. I sat on the ramp for a long time, waiting for
> traffic to clear so I could enter the roundabout. It reminded me of
> the old traffic circles in NJ.

Gee, you're not thinking of Garden State Pkwy. exit 135, are you?

--
Steve Alpert
MIT - B.S. '05, M.S. (Transportation) '06
http://web.mit.edu/smalpert/www/roads

Larry Gross

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Oct 18, 2005, 2:59:25 AM10/18/05
to
I take it that these roundabouts are used only for diamond interchanges
not full cloverleafs ... right?

so why not upgrade a diamond
to a cloverleaf instead of adding
roundabouts?

is it the lack of available land for
a full cloverleaf?

In other words... when/where/how
would a roundabout be considered
an optimal design and when not?

.. or am I missing something?

John Lansford

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Oct 18, 2005, 5:23:59 AM10/18/05
to
"Larry Gross" <gross...@gmail.com> wrote:

>I take it that these roundabouts are used only for diamond interchanges
>not full cloverleafs ... right?

Right

>so why not upgrade a diamond
>to a cloverleaf instead of adding
>roundabouts?

A cloverleaf interchange is a bad design when there are a lot of
vehicles using the two adjacent loops. The weaving section is too
short and traffic backs up on both the surface street (bad idea) and
the freeway (really bad idea). The progression is usually
cloverleaf/parclo/diamond/add traffic signals at the ramp termini.

>is it the lack of available land for
>a full cloverleaf?
>
>In other words... when/where/how
>would a roundabout be considered
>an optimal design and when not?

Roundabouts work when the traffic flowing through them is less than
around 22,000 vpd for a single lane roundabout. More than that and
the circles start backing up. They eliminate the need to widen the
bridge over the freeway for left turn lanes; it can remain two lanes
wide, so often adding the roundabouts as a retrofit can save a lot of
money.

Larry Gross

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Oct 18, 2005, 7:16:27 AM10/18/05
to
Take a look at this map:

http://maps.google.com/mapsq=massaponax&ll8.239191,77.498202&sll=38.240119,77.633679&sn=0.008166,0.018306&sspn=0.017190,0.038538&l=en

or just put Massaponax into GOOGLE MAPs

it looks like a diamond with one corner a clover?

the traffic count far exceeds 30K... probably 50-70

but note the footprint constraints.. upper and lower right.. (relative
to the interchange).

what to do?

traffic is now backing up not only on the
Route 1 surface strees because of signals
but traffic now backing up at the southbound
exit ramp...

is this a re-design or a re-locate? or what?

John F. Carr

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Oct 18, 2005, 10:36:15 AM10/18/05
to
In article <1129618765.2...@g44g2000cwa.googlegroups.com>,

Larry Gross <gross...@gmail.com> wrote:
>I take it that these roundabouts are used only for diamond interchanges
>not full cloverleafs ... right?
>
>so why not upgrade a diamond
>to a cloverleaf instead of adding
>roundabouts?

The purpose of a cloverleaf is to allow continuous flow of traffic
by avoiding at-grade crossings. If stopping traffic is acceptable
a cloverleaf is not necessarily an "upgrade" from a diamond.

--
John Carr (j...@mit.edu)

John Lansford

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Oct 18, 2005, 6:14:12 PM10/18/05
to
"Larry Gross" <gross...@gmail.com> wrote:

Rebuilding or upgrading an interchange in an area that has already
developed around it is difficult and expensive. Sometimes it's just
not possible. I could not get the link to work and the name you
suggested got me a bunch of hits but none near an interchange.

Marc Fannin

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Oct 18, 2005, 6:18:19 PM10/18/05
to
John F. Carr wrote:

> Larry Gross <gross...@gmail.com> wrote:
>
> >I take it that these roundabouts are used only for diamond interchanges
> >not full cloverleafs ... right?
> >
> >so why not upgrade a diamond
> >to a cloverleaf instead of adding
> >roundabouts?
>
> The purpose of a cloverleaf is to allow continuous flow of traffic
> by avoiding at-grade crossings. If stopping traffic is acceptable
> a cloverleaf is not necessarily an "upgrade" from a diamond.

It is if left turns are eliminated, and traffic is only stopping for
one direction of cross traffic instead of two....

(For those who don't know about them,
http://www.kurumi.com/roads/interchanges/ [U.S.]
and
http://www.cbrd.co.uk/reference/interchanges/ [U.K.]
are good general resources.)

________________________________________________________________________
Marc Fannin|musx...@kent.edu or @hotmail.com| http://www.roadfan.com/

Scott M. Kozel

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Oct 18, 2005, 7:21:11 PM10/18/05
to
John Lansford <jlns...@bellsouth.net> wrote:
>
> "Larry Gross" <gross...@gmail.com> wrote:
>
> >Take a look at this map:
> >or just put Massaponax into GOOGLE MAPs
> >it looks like a diamond with one corner a clover?
> >the traffic count far exceeds 30K... probably 50-70
> >
> >but note the footprint constraints.. upper and lower right..
> >(relative to the interchange).
> >what to do?
> >
> >traffic is now backing up not only on the
> >Route 1 surface strees because of signals
> >but traffic now backing up at the southbound
> >exit ramp...
> >is this a re-design or a re-locate? or what?
>
> Rebuilding or upgrading an interchange in an area that has already
> developed around it is difficult and expensive. Sometimes it's just
> not possible. I could not get the link to work and the name you
> suggested got me a bunch of hits but none near an interchange.

I-95 at Massaponax crosses US-1 on a fairly sharp skew, and two of the
quadrants would be difficult to expand without acquiring a lot of
expensive right-of-way.

Here's the Terraserver image of the area - http://tinyurl.com/8p7st

The I-95/US-1 interchange is in the center of the image.

The highway that crosses I-95 near the bottom of the image, is the US-17
Bypass. It has been proposed to widen US-17 to 4 lanes, and to build an
interchange between US-17 and I-95. This would considerably relieve
traffic on the I-95/US-1 interchange 1/2 mile away, in addition to
connecting US-17 Bypass directly to I-95.

Arif Khokar

unread,
Oct 18, 2005, 7:52:33 PM10/18/05
to
John Lansford wrote:

> Roundabouts work when the traffic flowing through them is less than
> around 22,000 vpd for a single lane roundabout.

Once more drivers get used to single lane roundabouts, would you
consider multi-lane roundabouts a viable option?

Scott Onson

unread,
Oct 18, 2005, 8:04:15 PM10/18/05
to

"Michael G. Koerner" <mgk...@dataex.com> wrote in message
news:kKqdnRC7-e7ZJs7e...@athenet.net...

> There have been roundabouts at an I-70 interchange in Vail, CO for many
> years now, too.
>

I can definitely confirm that all of the interchanges there and (I believe)
in Eagle also.

Scott Onson
was Wausau, now Platteville


Adam Prince

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Oct 18, 2005, 8:50:14 PM10/18/05
to

jdunlop wrote:


> I have some pictures at the office that I took in January, and
> eventually they'll go on the web, on our roundabout web page (don't
> bother looking for it right now, it doesn't exist yet, it's a
> relatively low priority.) If you're interested, I have pictures of
> most of the roundabouts in the state.

Sure!

>
> Anyway, I believe the one at Prosperity Church Road will have six
> roundabouts, three on either side of the interstate at each crossroad.
> Must simpler than the plan to combine some of the side roads, and works
> better than signalizing the intersections.

If i am nto mistaken, those were specifically asked for by either the
nearby community or something to that effect.

Paul DeRocco

unread,
Oct 18, 2005, 9:20:48 PM10/18/05
to
> "Larry Gross" <gross...@gmail.com> wrote

>
> I-485 roundabouts to keep traffic moving
>
> If roundabouts are your thing, you'll get a chance to circle them at
> three future interchanges on Interstate 485.
>
> Admittedly these one-lane roundabouts will take some getting used to,
> but I think drivers will come to appreciate how they keep traffic
> moving.
>
> Roundabouts, what few we have, are usually found on less-traveled roads
> where they eliminate the need for traffic signals and reduce
> collisions.
>
> The state is building a roundabout on each side of three outerbelt
> exits to avoid installing ramp traffic signals, usually a serious
> choke-point for traffic.
>
> http://www.charlotte.com/mld/observer/12915680.htm
>
> does anyone have a pix or graphic of one of these critters?
> are these interchange ramps SPUIs?

No. The description sounds pretty complicated, but it appears they're
talking about pairs of small roundabouts on each side of the freeway.

The Boston area frequently uses a single roundabout (aka rotary) under or
over a freeway (aka expressway), which work pretty well. See

<http://maps.google.com/maps?ll=42.241672,-71.025925&spn=0.007123,0.016002&t=k&hl=en>
I-93 south of Boston

<http://maps.google.com/maps?ll=42.419687,-71.103280&spn=0.007103,0.016002&t=k&hl=en>
I-93 north of Boston

<http://maps.google.com/maps?ll=42.525128,-71.080685&spn=0.007091,0.016002&t=k&hl=en>
I-95 north of Boston

<http://maps.google.com/maps?ll=42.499504,-71.157246&spn=0.007094,0.016002&t=k&hl=en>
I-95 north of Boston

<http://maps.google.com/maps?ll=42.223560,-71.170979&spn=0.007125,0.016002&t=k&hl=en>
I-95 southwest of Boston

and a particularly cool one with two interior ramps on I-95 west of Boston:

<http://maps.google.com/maps?ll=42.371497,-71.268847&spn=0.007108,0.016002&t=k&hl=en>

--

Ciao, Paul D. DeRocco
Paul mailto:pder...@ix.netcom.com


pigst...@yahoo.com

unread,
Oct 18, 2005, 10:18:31 PM10/18/05
to

> >
> >
> >
> >
> > I made the mistake of getting off I-70 eb at the one that is under
> > contruction at Rifle. I sat on the ramp for a long time, waiting for
> > traffic to clear so I could enter the roundabout. It reminded me of
> > the old traffic circles in NJ.
>
> Gee, you're not thinking of Garden State Pkwy. exit 135, are you?
>
> --
> Steve Alpert
> MIT - B.S. '05, M.S. (Transportation) '06
> http://web.mit.edu/smalpert/www/roads


I know you have mentioned it before, but I am not that familiar with
that one, but I am very familiar with the old Little Ferry Circle,
Bayway Circle, Raritan Circle, Green Street Circle, and a few others in
the wonderful Garden State.

James W Anderson

unread,
Oct 18, 2005, 10:41:15 PM10/18/05
to
The US 20 (Tavern Rd)/MA-128 interchange is lopsided, not like the one
in France that I saw on the Tour de France coverage in 2003.

That one was symmetrical, and the exiting and entering traffic from the
cross road had to enter the roundabout before entering the freeway, and
if making a 'left' onto the freeway had to go, using the roundabout
itself, under that freeway first then find the desired entrance to the
freeway before leaving the roundabout itself.

Larry Harvilla

unread,
Oct 19, 2005, 2:56:02 AM10/19/05
to
Michael G. Koerner wrote:

> There have been roundabouts at an I-70 interchange in Vail, CO for many
> years now, too.


There are roundabouts at exits all throughout Colorado and Utah, at the
very least. There are several in the mountains along I-70 in Colorado,
and I-15 south of I-70 in Utah has quite a few of them as well. In fact,
exit 4 off of I-15 in St. George, UT, is what I would call a "dog-bone"
or double-roundabout interchange.

--
Larry Harvilla
e-mail: roads AT phatpage DOT org
blog-aliciousness: http://www.phatpage.org/news/

also visit: http://www.phatpage.org/highways.html
(in progress)

John Lansford

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Oct 19, 2005, 5:12:23 AM10/19/05
to
Arif Khokar <akhok...@wvu.edu> wrote:

Possibly. They require a different mindset to overcome the confusion,
though, and the states need to set up a consistant procedure for how
to sign and stripe multilane roundabouts before they become
widespread.

Larry Gross

unread,
Oct 20, 2005, 3:43:16 AM10/20/05
to
One of the things I'm hearing is that roundabouts only "work"
up to a traffic count threshold and then they "fail".

... but then I also hear that roundabouts work better at metering
traffic than signals.

so... if a roundabout won't work because the traffic count is too
high...
do signals work "better" ....once the traffic flow threshold is
reached?

and two other questions:

can roundabouts be signalized on a demand basis? In other words, it
functions in static mode without signals but once the traffic count
threshold is reached then the signals turn on and take over... and then
once rush hour is over with.. it reverts back to an unsignalized
roundabout.
(thinking of situations where peak hour exceeds the roundabout metering
and not situations where the base flow is almost always above the
roundabout threshold).

... and how about traffic signals (without roundabouts) that function
this way...i.e.
traffic flow is metered and the default low-traffic mode is blinking
yellow/red
and once a threshold is reached - full signalization - alternates
red/green
kicks in.. and then once rush hour over.. back to blink mode....

John Lansford

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Oct 20, 2005, 5:11:48 AM10/20/05
to
"Larry Gross" <gross...@gmail.com> wrote:

>One of the things I'm hearing is that roundabouts only "work"
>up to a traffic count threshold and then they "fail".
>
>... but then I also hear that roundabouts work better at metering
>traffic than signals.
>
>so... if a roundabout won't work because the traffic count is too
>high...
>do signals work "better" ....once the traffic flow threshold is
>reached?

Yes, they do. A signalized intersection may fail once it reaches
capacity, but at least traffic will still move through it (albeit
slowly). When a roundabout fails, no one moves through it at all.

>and two other questions:
>
>can roundabouts be signalized on a demand basis?

No. Signalizing a roundabout defeats the purpose of moving the traffic
through the intersection smoothly.

>... and how about traffic signals (without roundabouts) that function
>this way...i.e.
>traffic flow is metered and the default low-traffic mode is blinking
>yellow/red
>and once a threshold is reached - full signalization - alternates
>red/green
>kicks in.. and then once rush hour over.. back to blink mode....

Obviously that is better than forcing someone to wait while a phase
goes unused, as what happens on a timed system. Actuated signals are
more efficient than timed ones.

Michael Moroney

unread,
Oct 21, 2005, 4:02:38 PM10/21/05
to
I've read they're building 5 roundabouts over a short distance on NY 67,
including 2 at the interchange with the Northway (I-87), which was a
diamond. They're building something there, but I saw it when they were
just starting work and I couldn't tell what they were doing.

I've heard the two roundabouts at the ends of diamond ramps called a
"dogbone" interchange.

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