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Thread: Single point urban interchange (SPUI) good, bad or otherwise?

  1. #1
    Cyburbian
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    Single point urban interchange (SPUI) good, bad or otherwise?

    What are people's thoughts/experience with single point urban interchanges (SPUI)? In theory, and application I suppose, they certainly conserve right-of-way in tight urban situations, yet they're admittedly confusing, at least the first couple of times newbies drive through them.

    Also, my sketch analysis (see image) of pedestrian crossings/conflict points tells me they're not conducive to a pedestrian environment, nor necessarily an a safe/predictable driving environment .. access management anyone? Thoughts?


  2. #2
    Cyburbian transguy's avatar
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    They seem to be the preferred treatment in some areas. They seem like a reasonable solution in many areas. However, I would agree that they should be avoided if non-motorized (i.e. ped) movements are prevalent in the area. They seem to be a very efficient way to move cars and trucks. I worked with a municipality awhile back who was trying to fight the local DOT from putting a SPUI into an area of their town. They ended up relying heavily on Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities: An ITE Proposed Recommended Practice to find an alternative solution (that I can't seem to remember right now).

    As far as confusion goes, after you drive through one a couple of times you won’t even necessarily realize that it is different. Clear signage and markings make them pretty easy to navigate.

  3. #3
    There is certainly an element of confusion with them. We have one here in town and 5 years after the install I still see people not able to follow their lanes through it. That could also be a function of the design of this specific interchange however as it is on a slight curve and there were some design compromises that had to be done that don't work so well such as a lane drop immediately outside of the intersection. That being said, it seems to function pretty well in terms of processing traffic.

    For pedestrians moving along the arterial, I would say it is an improvement over what was there before as they only have to look for traffic from a single direction at a time and cross at most two lanes at any one time as there are splitter islands at the base of each ramp. There is no crossing the arterial at the interchange however, nor would I want to try and get across the 10 lanes that are there. Instead pedestrians would need to go to the next signal in either direction in order to cross the arterial. Given the land use at the interchange, this might require some additional walking in some cases, but for the most part it would not take anyone much out of their way.

  4. #4
    Cyburbian Otis's avatar
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    I've only experienced one, and it seems to work well. People who haven't used them come to the interchange expecting something else, but as long as they pay attention to the lane markings and signals it works.

  5. #5
    Cyburbian
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    Oops, forgot image in original post

    Last edited by NHPlanner; 31 Mar 2008 at 1:39 PM. Reason: fixed image link

  6. #6
    Forums Administrator & Gallery Moderator NHPlanner's avatar
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    There's one in my hometown, and it works very well.

    Intersection of I-93 and US Rt. 3 Concord, NH:



    "Growth is inevitable and desirable, but destruction of community character is not. The question is not whether your part of the world is going to change. The question is how." -- Edward T. McMahon, The Conservation Fund

  7. #7
    Cyburbian Random Traffic Guy's avatar
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    I haven't looked to see how the guides show to design ped accommodations, but in your sketch shown there's only the right-turn lane crossing which is not controlled by the signal. The others will have standard gaps as the signal cycles, and with only 2 lanes to cross should be fairly quick and simple to cross, as others have indicated.

  8. #8
    Just judging from the sketch and photo, these would be the kiss of death for pedestrians. Cars won't slow to let them get across, it puts high speed traffic too close to sidewalks, its a long way across these things to get to any place. I wouldn't want to cross one.

  9. #9
    Cyburbian Random Traffic Guy's avatar
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    Only the right-turn crossings would be uncontrolled, i.e. the top and bottom ones shown on the drawing. The six crossings in the center of the drawing could all have pedestrian phases where no vehicles are moving across the crosswalk, with a pedestrian signal, etc.

    Long way across is a function of the highway width, same for this as for any normal diamond interchange. With the small width to cross at each point and having to watch only one direction of traffic if you don't trust the signals, to me this is easier to cross than the standard diamond interchange.

    Edit: on the picture NHPlanner posted, you can see some of the ped signals. Rectangular orange boxes at a mid level between the street and the vehicle signals.

  10. #10
    Cyburbian Iron Ring's avatar
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    SPUI's can be much more expensive to construct since the structure is usually much larger than a tight-diamond interchange (if the minor road goes over the highway). This cost can be offset by reduced property requirements.

    They can make sense when property is limited and they are well suited for double left/right turn lanes. I think the ped issue can be dealt with if it is a major concern. I agree that the example shown is not a very ped friendly situation.

  11. #11
    Cyburbian DetroitPlanner's avatar
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    SPUIs increased cost to design can be offset in many areas where ROW is at a premium. These structures are huge when you compare them to what they replaced. They do however have a much smaller footprint.

    I would agree that pedestrian and bicycles users must get frustrated with these at times. You can get some of the conflict out of them by increasing the amount of 'all red' time, but not all of the conflict. In my area I've observed that these have been implemented in areas that do not see a lot of pedestrian activity.

    The same is true for roundabouts. This is what makes transportation planning interesting (and frustraating). you always have to give up something to get something. The apathetic public just wants stuff fixed. The folks who are safety zelots want roundabouts everywhere, yet roundabouts are terrible for kids who have to cross streets (but good as less folks have injury accidents in areas with as you can't have t-bone crashes in a roundabout).

    It would be nice if we could come up with something that is safe, cheap, moves all people and goods quicker at all hours of the day and reduces pollution or tightens up development. Its tougher than hearding cats! Apathy, people wanting to control the process for their own benefit, and even planners and engineers that have wildly different viewpoiints makes it diffucult.
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  12. #12
    Quote Originally posted by Random Traffic Guy View post
    Only the right-turn crossings would be uncontrolled, i.e. the top and bottom ones shown on the drawing. The six crossings in the center of the drawing could all have pedestrian phases where no vehicles are moving across the crosswalk, with a pedestrian signal, etc.
    .

    I walk everywhere, and perhaps only get in a car every couple of weeks or so. I can tell you that uncontrolled right turn crossings are hell to navigate: cars think they have the right of way. And don't get me started on people on cell phones.

    I have also noticed that while you could have good signals for pedestrians, traffic engineers seem to always say "yes but htey are not appropriate in this spot."

  13. #13
    Cyburbian jmello's avatar
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    If the design speed of the SPUI was reduced, you could eliminate the wide channelized right turns and improve the pedestrian safety at the interchange. I agree that unsignalized channelized right-turns are very dangerous for pedestrians to cross.

  14. #14
    Cyburbian mgk920's avatar
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    WisDOT (Wisconsin Department of Transportation) never got interested in SPUIs. They did propose a few for US 41 upgrades here in the Appleton area over the past 20 years or so but decided against using them and there is only one in the state that I am aware of (the US 12/53/WI 93 interchange in Eau Claire has a SPUI mixed in). However, they have since gone hog wild over 'modern' roundabouts. Would they work in your setting?

    Mike

  15. #15
    Cyburbian jmac's avatar
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    Quote Originally posted by Margin Walker View post
    There is certainly an element of confusion with them. We have one here in town and 5 years after the install I still see people not able to follow their lanes through it. That could also be a function of the design of this specific interchange however as it is on a slight curve and there were some design compromises that had to be done that don't work so well such as a lane drop immediately outside of the intersection. That being said, it seems to function pretty well in terms of processing traffic.
    There is something a little strange about the SPUI in your fair city (my in-laws live there, so I visit a few times a year). I think your point about the horizontal curve is right on, especially since the expressway passes over the cross street on structure. These two issues make it somewhat difficult to see the "single point" in the interchange. I think the DOT updated the signing at some point, so it seems less confusing now than it did after it first opened.

    I did some preliminary SPUI designs for a corridor planning study at my previous office. The corridor is a fairly dense, suburban commercial area. Operationally, the SPUIs could move a lot of traffic, but there were definitely pedestrian and bicycle safety concerns.

    I do know that SPUIs were fun to draw, and even more fun to talk about. SPOOO-EEE. SPEW-EEE.

  16. #16
    Cyburbian
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    reply to WisDOT question

    I'm not sure how keen TDOT is on using SPUI's, or perhaps a "dumbbell" interchange like the UK ones illustrated here. I know roundabouts generally win the safety argument (not necessarily any reduction in number of crashes, but certainly intensity (fender bender vs. totaled car) However, they're a non-starter if you've got constrained right-of-way (the specific case I'm concerned with is an existing neighborhood, backing up to a regional shopping center.[

    Still, in my experiences driving on Australian and New Zealand road, in addition to having been a passenger on UK roads (generally considered the world's safest) they're safe and handle traffic pretty well.





    This site below highlights a dumbbell interchange, etc.

    Warrington New Town, UK

    http://images.google.com/imgres?imgu...icial%26sa%3DN

  17. #17
    Cyburbian Iron Ring's avatar
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    For those of you more interested in SPUI's there is a seminar on this subject available for download/streaming here:

    http://www.cts.pdx.edu/seminars.htm

    You need to look in the archive to teh Fall 2006 Seminar Series (Dec 1 - "Tight Diamond Interchange Versus Single Point Urban Interchange: Lessons Learned")

    As I recall the presentation was pretty dry and the speaker is a admitted SPUI 'super-fan', but there is plenty of information there if you can get through it.

  18. #18
    Cyburbian
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    Here's some images of the specific area in question.

    Also, what are the general dimensions (R.O.W.) needed for a SPUI? I'll take a look at that webinar, so thanks for sending the link along.



    Last edited by NHPlanner; 01 Apr 2008 at 3:53 PM. Reason: fixed image links

  19. #19
    Cyburbian mgk920's avatar
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    That does look like a good place for a SPUI - a place with a very narrow freeway ROW to work with. I have always thought that SPUIs are best for very tight urban situations where ROW is at a heavy premium (thus the 'U' in that acronym). You can place the on and off ramps right next to the freeway mainline within the existing ROW using retaining walls and the SPUI itself will function like a conventional surface street intersection with non-interfering left turns, the big advantage of the SPUI. The bridge taking the freeway over the cross street will have to be lengthened, too, but that will likely have to be re-engineered anyways whatever option is chosen.

    Good luck!

    Mike

  20. #20
    Cyburbian
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    Yeah, my guess is that this is all technically feasible, but the politics and NIMBYism are likely to be legendary. Still, the bridge and interchange are crucial components of any future development (2-acre lot subdivsion or corporate campuses) on Bells Bend (western side of river).

    This link could also free up regional highway capapcity (I-40 and Briley Parkway/SR-155), by providing an all-surface street route option for the the river bend and points in between. There would also be a VMT stabilization/reduction benefit by providing a more direct route option.

    The proposed project's still so relatively big and new, I'm not quite sure what to make of it yet. I do know that 2-acre lot subdivsions are a dime-a-dozen and something that's ultimately a money-drain for the city/county. Take a look if interested. One figure I've seen is 60,000 ADT estimated within 10-15 years; the only significant road on the river bend running north-south (Old Hickory Blvd.) is a narrow, 2-lane rural road, so I'm grappling with how to develop a cross section that:

    a) maintains a "rural" feel (i.e. swale vs. curb & gutter, minimal lighting, etc.)
    b) moves traffic volumes at a reasonable pace
    c) limits development along the road (this is the elephant in the room, both access management and the larger question of using transfer-of-development rights, conservation easements to prevent intense residential development, a.k.a. DRIVEWAYS every 50', on the northern section)

    Take a look if interested.

    http://www.maytowncenter.com/

    Check out page 21 especially:

    http://www.nashville.gov/mpc/pdfs/ma...s_March_25.pdf

  21. #21
    Cyburbian njm's avatar
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    Rochester, NY Area

    NYDOT is looking into the diverging diamond and SPUI at an interchange in the southern suburbs of Rochester, NY. They may have interesting information Here
    What luck! A random assemblage of words never sounded less intelligent.

  22. #22
    Cyburbian jmello's avatar
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    Quote Originally posted by Tall Fella' View post
    ...I'm grappling with how to develop a cross section that:

    a) maintains a "rural" feel (i.e. swale vs. curb & gutter, minimal lighting, etc.)
    b) moves traffic volumes at a reasonable pace
    c) limits development along the road (this is the elephant in the room, both access management and the larger question of using transfer-of-development rights, conservation easements to prevent intense residential development, a.k.a. DRIVEWAYS every 50', on the northern section)
    Here are some photos of a context sensitive freeway (Route 138) that connects two bridges on Conanicut Island in my home state of Rhode Island. It maintains a rural feel through the use of wooden guard rails and extensive landscaping, while also limiting access and providing unimpeded mobility through the corridor. I really love this design. The unrealistic 40MPH speed limit was a compromise made by the state to quell opposition from residents and the town government.










  23. #23
    Cyburbian
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    Thanks NJM and Jmello!

    Hey,

    Thanks for the NYDOT link, plus the cool photos of the RI parkway. Was this road built, or at least advertised and sold, as a parkway? Also, you mentioned a 40 mph posted speed limit; are actual speeds closer to 55-60 mph? Looking at the photos, that's my guess.

  24. #24
    Cyburbian jmello's avatar
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    Quote Originally posted by Tall Fella' View post
    Was this road built, or at least advertised and sold, as a parkway? Also, you mentioned a 40 mph posted speed limit; are actual speeds closer to 55-60 mph? Looking at the photos, that's my guess.
    It was built in 1993-94. I believe that the first design included jersey barriers, metal guard rails, obtrusive signs and little landscaping. After push back from the town and residents, the state compromised and designed it more as a parkway. It was still called an expressway (New Englanders don't use the word freeway). Prevailing speeds on this road are somehwere around 50-55MPH (New Englanders also don't drive very fast).

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