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Author Topic: Contraflow left-turn intersection  (Read 3399 times)

tradephoric

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Re: Contraflow left-turn intersection
« Reply #25 on: May 31, 2018, 03:02:10 PM »

A presentation out of North Carolina that discusses the design of NC-54 with the focus on maintaining good signal progression.  This presentation was tailor made for me.  It even has slides explaining "Why Parclo B is Better".



http://letsgetmoving.org/cms/wp-content/uploads/2016/04/NC-54-designing-for-progression-from-Hummer-100516.pdf

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jakeroot

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Re: Contraflow left-turn intersection
« Reply #26 on: May 31, 2018, 05:09:42 PM »

This presentation was tailor made for me.

That's an understatement. If I didn't know better, I'd say you created the presentation!

Only thing I disagree with is the "all crossings signal-controlled" bit. Typical B4's, with merges or yields for the off-ramp, require drivers to give way to pedestrians. The signalised variation (without free-flow ramps) is less common, and usually more expensive to build since cloverleafs are more easily modified into the traditional free-flow design (and are often the reason the B4 exists -- prior cloverleafs).

Here in Tacoma, our B4 (former cloverleaf) operates without pedestrian crossings. A separate bridge was constructed for pedestrian crossings. But, if crosswalks were added today, this is how it would work out for pedestrians:



FWIW, this is by far the best interchange in the city. I have never been stuck in traffic on it -- ever. Can't say that for any other interchange.
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NE2

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Re: Contraflow left-turn intersection
« Reply #27 on: May 31, 2018, 05:31:37 PM »

That's a SPUI with two loops. There's one with one loop at the south end of the Liberty Tunnel in Pittsburgh.
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johndoe

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Re: Contraflow left-turn intersection
« Reply #28 on: July 28, 2018, 05:01:25 PM »

In this PDF NCDOT talks about a "double contraflow intersection" where both grade separated routes get the unique left-turn treatment:
https://www.ncdot.gov/news/public-meetings/Documents/U-5301_Handout_Consolidated_Final.pdf
see sheet 4/14


And notice in southeast quadrant this alternative seems to require the demolition of Peak Auto  :bigass:
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TheHighwayMan394

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Re: Contraflow left-turn intersection
« Reply #29 on: July 28, 2018, 05:08:30 PM »

Wendy's would also be inbetween an off-ramp and a freeway. Convenient for roadgeeks, but probably frowned on by FHWA.
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jakeroot

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Re: Contraflow left-turn intersection
« Reply #30 on: July 28, 2018, 06:55:50 PM »

Jesus, that's complex! Not too keen on those awkward merges from the overpass onto US-64, though. Does look to be pretty easy to configure for pedestrian crossings, however.
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johndoe

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Re: Contraflow left-turn intersection
« Reply #31 on: July 29, 2018, 10:09:27 AM »

Jesus, that's complex! Not too keen on those awkward merges from the overpass onto US-64, though. Does look to be pretty easy to configure for pedestrian crossings, however.
Yeah I wonder if they're thinking of them as "ramps",  notice they have signals.  I wish their image would have ped  crossings in another color.

Also this isn't an interstate highwayman, so I'm not sure how much FHWA has to approve.
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Joe The Dragon

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Re: Contraflow left-turn intersection
« Reply #32 on: July 30, 2018, 03:33:51 PM »

In this PDF NCDOT talks about a "double contraflow intersection" where both grade separated routes get the unique left-turn treatment:
https://www.ncdot.gov/news/public-meetings/Documents/U-5301_Handout_Consolidated_Final.pdf
see sheet 4/14


And notice in southeast quadrant this alternative seems to require the demolition of Peak Auto  :bigass:
what a way to be messup a nice overpass with the left turns.
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jakeroot

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Re: Contraflow left-turn intersection
« Reply #33 on: July 30, 2018, 05:07:43 PM »

what a way to be messup a nice overpass with the left turns.

Not sure exactly what you mean, but no matter how they're configured, overpasses can seriously improve the flow through an area.
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Joe The Dragon

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Re: Contraflow left-turn intersection
« Reply #34 on: July 30, 2018, 05:24:12 PM »

what a way to be messup a nice overpass with the left turns.

Not sure exactly what you mean, but no matter how they're configured, overpasses can seriously improve the flow through an area.
yes but when other plans have them with ramps why build it like the kills grade separated flow on the main line.
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jakeroot

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Re: Contraflow left-turn intersection
« Reply #35 on: July 30, 2018, 10:56:50 PM »

what a way to be messup a nice overpass with the left turns.

Not sure exactly what you mean, but no matter how they're configured, overpasses can seriously improve the flow through an area.

yes but when other plans have them with ramps why build it like the kills grade separated flow on the main line.

Service interchanges require all crossing maneuvers to be on one road, which helps traffic on the mainline, but really screws with the arterial (especially tight interchanges with poor storage capacity). The interchange above really doesn't even need signals, so it's actually pretty clever. I also don't get the feeling that US 64 is supposed to be a full-blown freeway through this area, so evening the flow between the two roads is actually pretty smart. Of course, if NCDOT did decide to make 64 free flow in the future, it is easily converted into a sort of Parclo A4 interchange (make the NE and SW roads two-way, and remove the left turns from Lake Pine Dr), a pretty high capacity interchange (so long as there's enough distance between the off-ramps).
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tradephoric

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Re: Contraflow left-turn intersection
« Reply #36 on: March 18, 2019, 02:25:55 PM »

This came up in the Michigan thread.  MDOT is proposing building a DDI at the I-75/Big Beaver interchange as part of the I-75 modernization project.  I personally feel like this interchange would have been a perfect candidate for a contraflow Parclo as the wide medians along Big Beaver would allow space for the contraflow lefts.  Below is the DDI being proposed along with a model of the Contraflow Parclo:



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