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Thread: "Inverted/reverse" roadway median?

  1. #1
    Cyburbian
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    "Inverted/reverse" roadway median?

    I've got a development proposal that's discussing an "inverted/reverse" roadway median. Anybody heard of this before, and could you provide an image of this? A quick search turned up "Central reservation" on Wikipedia, with the comment below, but again, it's clear as mud to me.

    One median of note is the "inverted" median of the Golden State Freeway (I-5) in the Tehachapi Mountains between Los Angeles, California and the San Joaquin Valley. For several miles the median is inverted Northbound traffic is on the western roadway and southbound traffic on the eastern road.

  2. #2
    Cyburbian Richi's avatar
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    I don't have a clue. What is the reasoning behind it? I would think that it would only work on totally grade separated facilities. The only reason I can think for doing it would be to reduce grades in the direction of the heavy load traffic if it was imbalanced.

    I'd like to hear more if anyone out there has any experience with the idea.

  3. #3
    Cyburbian
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    I don't know the extent of the "inverted median" in the proposal you have, but one possibility is that this is similar to a "continuous flow intersection" designed to more efficiently serve very high left turn demands. I understand this has been done at a number of freeway interchanges with very specific and problematic turning movements, and it has been proposed for one interchange on the 427 in Toronto a couple of years ago, but nothing has come of it yet. The idea as I understand it is to get the traffic to swap sides through the area of difficulty so that left turns no longer have opposing traffic when they come to the intersection. Of course the more traditional method would be some sort of grade separation, but the structure is apparently deemed too expensive in some cases, and can be avoided if there is sufficient right-of-way. Could that be what you are looking at?

    As for the I-5 in California, thanks for the reference, it is an interesting case! My guess there wold be it is the result of a twining some years ago when due to the terrain, widening on the existing platform was just not possible, and geometry on the curvy alignment just made it simpler to swap directions for a while rather than try to keep traffic on the "correct" side when it really didn't matter. Does anyone have any history on this site?

  4. #4
    Cyburbian Random Traffic Guy's avatar
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    Doesn't ring a bell, except for the interchange shown below. Show us a pic if you can. I could see a few weird things making some sense if all development was forced to be on one side of a road, and the traffic patterns were predominately towards one way. But advantages not likely to outweigh the WTF factor.


  5. #5
    Cyburbian CJC's avatar
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    Quote Originally posted by Tall Fella' View post
    One median of note is the "inverted" median of the Golden State Freeway (I-5) in the Tehachapi Mountains between Los Angeles, California and the San Joaquin Valley. For several miles the median is inverted Northbound traffic is on the western roadway and southbound traffic on the eastern road.
    You're talking about the Grapevine here - and as another poster correctly assumed, this is done to reduce grades for truck traffic (I don't remember if it's lower for trucks going up or going down, but whatever is harder on trucks is diminished). It is strange looking over and seeing traffic on the wrong side of the valley.

  6. #6
    Cyburbian DetroitPlanner's avatar
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    RTC,

    Wow, that is the oddest SPUI I've ever seen. Do any of those actually exist?
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  7. #7
    Cyburbian jkellerfsu's avatar
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    Any chance we are talking about a median that collects water to treat water quality?

  8. #8
    Cyburbian Random Traffic Guy's avatar
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    Quote Originally posted by DetroitPlanner View post
    RTC,
    Wow, that is the oddest SPUI I've ever seen. Do any of those actually exist?
    Supposed to be built by now according to that graphic. I saved that when it was in the news about 2 years ago.

    Anyone in Kansas City? Does this thing exist?

    In theory it looks like it would work well. Not really a SPUI, in the same family maybe. The two signalized intersections are much simplified since it needs only two phases, so there's much less delay to the cross traffic. Exit ramp traffic never stops, unless the left turns back up from the other side's signal.

    However, has no provision for frontage road through traffic so it can't be used in the enlightened parts of the country with continuous frontage roads. Also, can't run both directions of cross-street traffic at one time, so coordination along the arterial may suffer.

  9. #9
    Cyburbian
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    SPUI variation

    Yeah, I'm with Detroit Planner, that's definitely a crazy spin on a single-point urban interchange (SPUI). In fact, there's one proposed for this site, in addition to another part of the city. Shoot, I'll start a thread on that, as I'm curious for thoughts.

  10. #10
    Member
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    I-90 center roadway

    On I-90 in Seattle, the segment that runs between Seattle and the City of Bellevue is referred to the center-reversable roadway because it basically operates one way (westbound) in the AM and one-way (eastbound) in the PM, hence the lanes are "reversable." These lanes are located in the center of the highway and separted from other lanes by a concrete barrier, thus it could be considered comparable to a median. WSDOT has done numerous studies of the roadway so there is lots of data/info about reversable lane performance, volumes, speed, etc.... Hope that helps.

  11. #11
    Cyburbian mgk920's avatar
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    Quote Originally posted by CJC View post
    You're talking about the Grapevine here - and as another poster correctly assumed, this is done to reduce grades for truck traffic (I don't remember if it's lower for trucks going up or going down, but whatever is harder on trucks is diminished). It is strange looking over and seeing traffic on the wrong side of the valley.
    There are several places in the USA where the roadways of a major divided highway are reversed. One is on I-85 in North Carolina, others are in downtown Binghamton, NY; near the airport in Miami, FL and on I-8 in western Arizona. There is also a notable one in Montreal.

    Mike

  12. #12
    Cyburbian jmello's avatar
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    Quote Originally posted by DetroitPlanner View post
    Wow, that is the oddest SPUI I've ever seen. Do any of those actually exist?
    Half of one exists in Providence, RI and has for 40+ years.


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