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
Roundabouts, what few we have, are usually found on less-traveled roads
where they eliminate the need for traffic signals and reduce
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.
does anyone have a pix or graphic of one of these critters?
are these interchange ramps SPUIs?
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
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.
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
___________________________________________ ____ _______________
Regards, | |\ ____
| | | | |\
Michael G. Koerner May they | | | | | | rise again!
Appleton, Wisconsin USA | | | | | |
___________________________________________ | | | | | | _______________
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.
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)
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.
Robert I. Cruickshank
roadgeek, historian, progressive
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.
River Falls, WI
> 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.
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
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.
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.
In pertinent part:
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
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
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:
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
i'm guessing the new grade separation/roundabout tandem has eliminated
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...
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
Froggie | Picayune, MS | http://www.ajfroggie.com/roads/
I have photos, but they're in my perpetual backlog...
> 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
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
but it could very well be an example of closing the barn door after the
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
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.
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
John Lansford, PE
The unofficial I-26 Construction Webpage:
This MDOT SHA news release announced the completion of a new Interstate
interchange that has roundabouts between the ramp terminals and the
"Good News for Prince George’s County Residents and Commuters"
"(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
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.
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.
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
It seems to me this one is too small to handle heavy volumes of traffic.
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
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.
>>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
>>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?
MIT - B.S. '05, M.S. (Transportation) '06
so why not upgrade a diamond
to a cloverleaf instead of adding
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?
>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
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
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
is this a re-design or a re-locate? or what?
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)
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.
> 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
> 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....
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
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.
> 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?
> 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.
was Wausau, now Platteville
> 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.
If i am nto mistaken, those were specifically asked for by either the
nearby community or something to that effect.
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
I-93 south of Boston
I-93 north of Boston
I-95 north of Boston
I-95 north of Boston
I-95 southwest of Boston
and a particularly cool one with two interior ramps on I-95 west of Boston:
Ciao, Paul D. DeRocco
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.
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.