SPUI or diverging Diamond?
Larry G
http://www.youtube.com/watch?v=_R5-7E17RTw&feature=related
SPUI
http://www.youtube.com/watch?v=mwpoPQ1SPJU&feature=related
I'm still trying to get my mind wrapped around the two that look
similar to me.
How would folks compare and contrast these two in terms of
functionality, safety, footprint, and cost?
other factors?
what are the parallel roads so far apart? could they not be in a much
tighter configuration in an area with a limited footprint ?
Ralph Herman
(in article
<ca0a9b6d-5cb4-430e...@u10g2000yqk.googlegroups.com>):
> diverging diamond
>
> http://www.youtube.com/watch?v=_R5-7E17RTw&feature=related
>
> SPUI
>
> http://www.youtube.com/watch?v=mwpoPQ1SPJU&feature=related
>
> I'm still trying to get my mind wrapped around the two that look
> similar to me.
>
> How would folks compare and contrast these two in terms of
> functionality, safety, footprint, and cost?
1. Functionality. Diverging diamonds (DD) work best where a majority of the
surface arterial traffic is coming from/going to the freeway mainline. Also
DD work best when one direction of thru traffic has a far greater load than
the opposite (such as an industrial park at peak times). SPUIs eliminate a
signal phase, and increase left turn traffic flow substantially, and is best
when traffic flow is generally equal on all approaches.
2. Safety. DDs are very safe, eliminate turning collisions at
intersections. Signal phasing is simplified. SPUI have a large "neutral
zone" in the center of the intersection, which requires a long "all red
phase" to clear the intersection.
3. Footprint. SPUIs generally have narrower footprints than diamond
interchanges. Retrofitting in a DD generally does not require modifications
on the bridge structures, but requires wider ROW on the surface arterial
approaches to the interchange to "cross over" the traffic flows.
4. Cost. DD are a "realitively" low cost modification... no bridge
modifications are needed. SPUIs are more expensive than traditional diamond
interchanges, due to the increased length of the bridge spans between piers.
DDs and SPUIs are NOT interchangeable, they serve different needs.
Ralph
Froggie
>
> 3. Footprint. SPUIs generally have narrower footprints than diamond
> interchanges. Retrofitting in a DD generally does not require modifications
> on the bridge structures, but requires wider ROW on the surface arterial
> approaches to the interchange to "cross over" the traffic flows.
However, that's countered by the fact that you typically need a wider
ROW on the surface arterial for the SPUI due to the turn lanes...often
a dual left turn lane plus a right turn lane.
Froggie | Alexandria, VA | http://www.ajfroggie.com/roads/
Ralph Herman
(in article
<f30c07e5-c46a-426d...@p1g2000yqm.googlegroups.com>):
>> On Oct 30, 10:59ï¿œpm, Ralph Herman <rlaher...@earthlink.net> wrote:
>>
>> 3. ï¿œFootprint. ï¿œSPUIs generally have narrower footprints than diamond
>> interchanges. ï¿œRetrofitting in a DD generally does not require modifications
>> on the bridge structures, but requires wider ROW on the surface arterial
>> approaches to the interchange to "cross over" the traffic flows.
>
> However, that's countered by the fact that you typically need a wider
> ROW on the surface arterial for the SPUI due to the turn lanes...often
> a dual left turn lane plus a right turn lane.
>
> Froggie | Alexandria, VA | http://www.ajfroggie.com/roads/
Froggie, you are correct about typically, and it only makes sense to insert a
SPUI within an existing interchange if traffic flows are substantially
improved. In most cases, DOTs now want to install or retrofit dual left turn
lanes at all their heavily traveled urban diamond interchanges, and if the
ROW exists, they will widen the surface arterial (and arterial overcrossing)
to accomodate the additional turn lanes.
Ralph Herman
jdunlop
Both provide similar operational benefits. The interchanges I've
analyzed so far lean towards the DDI. I've said publicly that I don't
think NCDOT will build too many more SPUIs in the future because the
DDI is less expensive and works better (in cases where you'd choose a
SPUI over, say, a standard diamond or partial clover.)
Ralph Herman
(in article
<954f6723-c7c5-49f4...@s4g2000yql.googlegroups.com>):
> On Oct 31, 11:45 am, Justin Rhodes <justinkrho...@gmail.com> wrote:
>> On Oct 31, 10:23 am, Ralph Herman <rlaher...@earthlink.net> wrote:
>>
>>
>>
>>
>>
>>> On Sun, 31 Oct 2010 05:38:10 -0700, Froggie wrote
>>> (in article
>>> <f30c07e5-c46a-426d-afcc-08ec3fff3...@p1g2000yqm.googlegroups.com>):
>>
>>>>> On Oct 30, 10:59 pm, Ralph Herman <rlaher...@earthlink.net> wrote:
>>
>>>>> 3. Footprint. SPUIs generally have narrower footprints than diamond
>>>>> interchanges. Retrofitting in a DD generally does not require
>>>>> modifications
>>>>> on the bridge structures, but requires wider ROW on the surface arterial
>>>>> approaches to the interchange to "cross over" the traffic flows.
>>
>>>> However, that's countered by the fact that you typically need a wider
>>>> ROW on the surface arterial for the SPUI due to the turn lanes...often
>>>> a dual left turn lane plus a right turn lane.
>>
>>>> Froggie | Alexandria, VA | http://www.ajfroggie.com/roads/
>>
>>> Froggie, you are correct about typically, and it only makes sense to
>>> insert a
>>> SPUI within an existing interchange if traffic flows are substantially
>>> improved. In most cases, DOTs now want to install or retrofit dual left
>>> turn
>>> lanes at all their heavily traveled urban diamond interchanges, and if the
>>> ROW exists, they will widen the surface arterial (and arterial
>>> overcrossing)
>>> to accomodate the additional turn lanes.
>>
>>> Ralph Herman
>>
>> One factor to consider as well is the inclusion of service/frontage/
>> feeder roads. SPUIs are able to accomodate service roads easily with
>> an additional signal phase. I'm not sure what would happen if service
>> roads were to be incorporated into the DDI design.- Hide quoted text -
>>
>> - Show quoted text -
>
> Also, what happens at a DDI in the event of a traffic signal failure
> due to a power outage, accident, etc? Navigation of a SPUI is
> intuitive, albeit somewhat slower as it mostly retains the
> characteristics of a typical 4 way intersection. I can see lots of
> driver confusion ensuing at a DDI in the event of a signal failure
Actually, I think a DD is a lot less confusing in case of a traffic signal
failure. A much smaller "neutral zone" with a DD, and lane markings and
regulatory signage is a lot simpler to post. The 2 "crossover (diverging)
intersections" are really nothing more than two one way streets intersecting
at lower speeds.
jdunlop
> On Sun, 31 Oct 2010 13:39:57 -0700, Justin Rhodes wrote
> (in article
>
> > Also, what happens at a DDI in the event of a traffic signal failure
> > due to a power outage, accident, etc? Navigation of a SPUI is
> > intuitive, albeit somewhat slower as it mostly retains the
> > characteristics of a typical 4 way intersection. I can see lots of
> > driver confusion ensuing at a DDI in the event of a signal failure
>
> Actually, I think a DD is a lot less confusing in case of a traffic signal
> failure. A much smaller "neutral zone" with a DD, and lane markings and
> regulatory signage is a lot simpler to post. The 2 "crossover (diverging)
> intersections" are really nothing more than two one way streets intersecting
Missouri's already had a power failure at the first DDI in
Springfield, and traffic handled it fine. As you pointed out (and
this is almost exactly what the MODOT engineers siad) the smaller
footprint of the "neutral zone" (I like that!) helps, plus it's an
either-or movement (one main street goes, or the other (the turns from
the ramp go with the appropriate main street move.) At a SPUI, you
have six different movements trying to access the same general space
(I understand the main street throughs don't cross, but given the
spacing, it's harder to judge when it's your turn.)
Larry G
is there any such thing as roundabouts instead of traffic signals for
these intersections?
jdunlop
>
> - Show quoted text -
Sure, however the volume of traffic going through probably means that
a two-phase signal will work better in most cases. There's some
scenarios, with traffic going heavily towards one side of the
interchange, where a roundabout on the "lighter" side might resolve
spacing problems with nearby intersections, as well as work better
than a signal.
James W Anderson
http://maps.google.com/maps?ie=UTF8&ll=40.376894,-111.818649&spn=0.000723,0.001231&t=h&z=19
Was shot a month before it was finished. Look just to the northwest
past the Park and Ride lot on the west side of the freeway it goes
over, and you'll see the 'bridge farm' just after the north span was
'harvested' and put into place. They were cleaning things up there
after their work, and so there's a lot of equipment still in the shot.
Follow I-15 down to the southeast to the next interchange, with U-180,
which will likely be labeled as '500 East', and they are putting
another one in. Last I saw a couple weeks ago the piers are in place
on either side of the old bridge for the new ones, which will also be
put in using Accelerated Bridge Construction methods.
Pete Jenior
"Larry G" <gross...@gmail.com> wrote in message
news:2413f244-e2d4-4afa...@t13g2000yqm.googlegroups.com...
Do you mean one roundabout (in the middle of a SPUI) or two roundabouts at
each ramp terminal at a regular diamond? I've seen a picture of the former,
but it was in Europe. The latter is becoming common in some places...here
are a couple of examples from MD. One advantage to using roundabouts at
interchanges is that storage for left turns isn't needed and the bridge can
be narrower.
Pete
James W Anderson
freeway, Happy Valley Road onn I-17.
St. George Utah, a metro area of I think still less than 100,000 has
one also on I-15, it's recent, has been redone once since even that, I
think I mentioned it before and how they had done the rotaries up in
Christmas lights when I saw it years ago once.
Have seen them in France where you enter the rotary, then you can go
right to go one direction and then circle around to get to the ramp to
go to the other. France as it is is roundabout central, over 25,000
all told, in the Tour de France, they don't go through the entire tour
without at least one one if not more tripping up a cyclist during the
course of its run.
One of the Versus commentators refers to them as 'road furniture'
although the term is used for any obstruction, curb, or other raised
item in or beside any road during the course of the race.
H.B. Elkins
>Do you mean one roundabout (in the middle of a SPUI) or two roundabouts at
>each ramp terminal at a regular diamond? I've seen a picture of the former,
>but it was in Europe. The latter is becoming common in some places...here
>are a couple of examples from MD. One advantage to using roundabouts at
>interchanges is that storage for left turns isn't needed and the bridge can
>be narrower.
Isn't there an interchange in Baton Rouge, La., where a circular bridge was
built above the freeway that serves as a de facto roundabout?
And as for the latter, which I've heard called "barbell" or "dumbbell"
interchanges, with a roundabout on each end, there are a number of those along
the former IND 431 north of I-465 in the Indianapolis suburb of Carmel.
--
To reply by e-mail, remove the "restrictor plate"
Larry G
> "Larry G" <gross.la...@gmail.com> wrote in message
Thanks for links... I guess I would have thought that a roundabout
for a SPUI would not work well since, in theory, the at grade
intersection have a greater capacity than a signalized at-grade
intersection and we know that roundabouts are limited to what .about
25K before they will fail?
I was thinking of two roundabouts on the diverging diamond - one at
each crossover.
ever seen one of them?
jdunlop
Expanding on my previous response, there's only 4 DDIs built and open
in the country (maybe a half-dozen under construction) so the direct
answer is no to your question, no roundabouts at any DDIs so far.
I did see a sketch of a DDI that included a roundabout at one of the
criss-cross intersections. The traffic is heavily skewed towards the
other direction of the interchange, and so the roundabout looked
feasible. It also provided a solution to providing access to a road
very close to the ramp intersection. All of this created what looks
like a five-leg roundabout. I didn't have a location, nor info about
if this particular project was going forward, so I don't have any more
details.
Larry G
Thanks... I did not realize that they were so new. How new are SPUIs?
Rich Piehl
Don't know if it's he oldest but there's a SPUI in St. Louis County, MO
that dates from the mid 80's
Marc Fannin
> Thanks... I did not realize that they were so new. How new are SPUIs?
The first opened in 1974, unless you count "Inner SPUI with left
exits", the interchanges where all four ramps meet in the middle
between the freeway's roadways. You can read about their history at
http://www.kurumi.com/roads/interchanges/spui.html - that's where I
extracted the date and the above term in quotes - and, using that page
as a start point, I found that past newsletters of the Institute of
Transportation Engineers have had articles on them (go to
http://www.ite.org/itejournal/ for details).
_________________________________________________________________________
Marc Fannin|musxf579 @hotmail.com|http://roadfan.com/ (m.t.r FAQ, etc.)
John Lansford
>Thanks... I did not realize that they were so new. How new are SPUIs?
SPUI's have been around for at least 10 years, perhaps even more. NC
has built several, most notably along I-40/85 and on I-540, although
there's a couple in Charlotte and one on US 70/Glenwood Avenue.
John Lansford, PE
--
John's Shop of Wood
http://wood.jlansford.net/
Ralph Herman
(in article <1tfad69u9rnmpgtpb...@4ax.com>):
First in US is believed to be in 1974 in Clearwater, FL, at the intersection
of SR 60 and US 19.
Ralph
James W Anderson
> On Nov 5, 7:05 pm, Larry G...wrote:
>
> > Thanks... I did not realize that they were so new. How new are SPUIs?
>
> The first opened in 1974, unless you count "Inner SPUI with left
> exits", the interchanges where all four ramps meet in the middle
> extracted the date and the above term in quotes - and, using that page
> as a start point, I found that past newsletters of the Institute of
>
> _________________________________________________________________________
> Marc Fannin|musxf579 @hotmail.com|http://roadfan.com/(m.t.r FAQ, etc.)
Japan's urban freeways have 'inner spui's throughout the system.
Depends on the road that the freeway is often over.
There are a few in Chicago, there is some footage on Youtube that one
of the shooters here shot, and it shows a couple.
First DDI is believed to be the Springfield MO I-44/MO-13 interchange,
but the first to be built from scratch after demolishing an old
interchange is more than likely the I-15/U-145 interchange in Utah,
the Dorsett Road interchange spoken of in this thread is a very close
second, only by days.
The Utah one is functioning very well. Last thing that needed to be
done was configure and install the ramp metering, that is now done as
I went through there about six last night and it was working
perfectly.