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Thread: Adding lanes on limited access highways: why from entrance ramps instead of from the left?

  1. #1
    Cyburbia Administrator Dan's avatar
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    Adding lanes on limited access highways: why from entrance ramps instead of from the left?

    I'm a planner, and I still find myself going "WTF?" at various traffic management practices.

    One of them is the way lanes are added to carriageways on limited access highways. In Ohio, at the point a limited access highway widens from two to three or more lanes, the new lanes are added not on the left, but from the continuation of entrance ramps on the right as a new traffic lane.. Whenever a limited access highway transitions from four lanes to three or three lanes to two, it's not by merging the leftmost traffic lane into the remaining leftmost lane, but by turning the rightmost traffic lane into an "exit only" lane for the next upcoming exit. This forces through traffic in the rightmost lane to merge left into the remaining traffic lane, causing confusion by drivers unfamiliar with the road, and inevitable congestion.

    So, those familiar with traffic management: why do they do this?
    Growth for growth's sake is the ideology of the cancer cell. -- Edward Abbey

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    Cyburbian hilldweller's avatar
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    There's nowhere to add a lane from the left in these parts, other-way traffic is almost always divided by a barrier of some sort. Even where we have grassy areas in between they are usually pretty narrow. But I think part of the answer is drainage.

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    Cyburbian DetroitPlanner's avatar
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    It might be to fool the EPA into thinking that these are safety improvements and not capacity improvements. I would need a lot more information to assess this. Do you happen to know if these are done in areas that are considered either out of conformity or in maintenance? Unless you're a transportation planner, I bet you have no idea. hmmmm I'll rephrase it.... is it in a big old stinky city or is it WAY out in a rural area (outside of the MPO boundary)?
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    Cyburbian wahday's avatar
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    I tend to think Hilldweller's response is the correct one. They do the same thing here with regards to transitioning from three to two (or four to three). Its interesting to drive in the next-to-left-most lane and see how many exits it is until you have to merge left to avoid exiting.

    As for on-ramps, though, I can see that there is some logic to giving those merging onto highway speed traffic a designated lane to get up to speed before moving left into the main flow. Getting on the Beltway in Washington DC is the opposite. On many entrance ramps there is a very short distance for you to get up to speed and merge left into what is often some intense traffic (and drivers that would really prefer you NOT merge in front of them). Its a very high stress situation.
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  5. #5
    Cyburbian
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    Hilldweller's right: the majority of limited-access roads aren't initially built with a wide space in the middle--free of Jersey walls, steep slopes, streams, and other barriers--that can be used for adding lanes, so when the time comes to do so, extending the merge lane is the simplest, and often the only, way to go. It also reduces the number of merges required at the point where the road widens. Once you adopt that solution to widen part of the highway, forcing the rightmost lane to peel off as a ramp at the next exit is again the only practical option, and you just get stuck with the inconvenience to drivers who don't want to take the exit.

    Still, on stretches of highway that do have wide medians w/o barriers (a few miles of the Baltimore Beltway around Lochearn, part of Route 24 south of Bel Air, here in MD), using the median to add lanes does sound a lot better, and cheaper, than buying/seizing land to widen the road's total ROW/footprint.

  6. #6
    Cyburbian RPfresh's avatar
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    I personally think adding lanes on the right is a worse idea than adding lanes at all. Santa Rosa is a suburb north of SF and has some of the worst non-commuter traffic in the bay, even though it is a smaller city, and the culprit is these third lanes that are entrance-exit only and end and begin each exit. Cars that are merging in and out of these lanes, as well as cars merging to the left to get away from that hell, slow down the traffic to a crawl, and this is in an area that isn't especially heavily populated. I'm sure this is pretty common. In my city we have an especially ridiculous situation - traffic clogs up our two-lane highway and magically dissipates after our only third entrance/exit right hand lane. If it were up to me I would run a test by blocking off these lanes and seeing if traffic sped up.

    As for why this happens, I would guess that a city administration wants to address 'the traffic problem' and the easiest way to visibly do this and show that they care is to add another lane, while it may not be the best option. But I'm not sure helping ease traffic is a good idea anyway, which is why I'm starting a thread that is sort of related to this.

  7. #7
    Cyburbian Doohickie's avatar
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    Quote Originally posted by hilldweller View post
    There's nowhere to add a lane from the left in these parts, other-way traffic is almost always divided by a barrier of some sort. Even where we have grassy areas in between they are usually pretty narrow. But I think part of the answer is drainage.
    I disagree- you can still do the beginning of a new lane or merger of a lane being ended on the left by creatively painting your lane stripes.

  8. #8
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    Adding a lane by doing it on the right as a ramp merges is more forgiving compared with a standard merging ramp. The merge conflict is eliminated.

    Deleting a lane by having it peel off at an exit is more forgiving compared with having the leftmost two lanes merge.

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