Is this a SPUI or Diamond interchange?

Started by SkyPesos, December 21, 2020, 01:42:34 PM

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SkyPesos

Posted this image in another thread already, but thought it would be better to ask about in its own thread instead of with another topic. There's this interchange type that a Chinese city I'm most familiar with (Fuzhou) use on almost every interchange on its 2nd ring road, and I want to know if there's a name for it.
Here are 2 images from Baidu maps; first on street view and the other on sattelite view. Sattelite view quality isn't the best, but the overpass is outlined.


It functions like a SPUI because of the single set of signals, but also a diamond interchange because of the through movement on the ramps. Is there a name for this, tight diamond? Traffic signal order is interesting as well. On the surface road, it's the standard both lefts green first, then both straight movements green that most SPUI's use. But on the ramps, both straight movement lights turn green first, allowing the left turn vehicles to pile onto the dotted yield lines (do those even exist in the states?) under the overpass, then after both straight movement turn red, the left turns turn green. What is the name for this type of interchange, and are there any examples of this in the states? I haven't seen any examples of this outside China.


jeffandnicole

Seems to be just an ordinary diamond.  Take out the overpass, and it'll be just an ordinary intersection.  The one direction has a leading protected turn; the other direction has a lagging protected turn.

Ned Weasel

Quote from: SkyPesos on December 21, 2020, 01:42:34 PM
It functions like a SPUI because of the single set of signals, but also a diamond interchange because of the through movement on the ramps. Is there a name for this, tight diamond? Traffic signal order is interesting as well. On the surface road, it's the standard both lefts green first, then both straight movements green that most SPUI's use. But on the ramps, both straight movement lights turn green first, allowing the left turn vehicles to pile onto the dotted yield lines (do those even exist in the states?) under the overpass, then after both straight movement turn red, the left turns turn green. What is the name for this type of interchange, and are there any examples of this in the states? I haven't seen any examples of this outside China.

SPUIs with straight-through movements from the ramps exist in the U.S., but they're exceptional cases.  This was discussed here:

https://www.aaroads.com/forum/index.php?topic=26915.msg2505748#msg2505748

I can show you two examples from my home state, one where there's a straight-through movement going to a frontage road: https://goo.gl/maps/1116LckxmMHvUVf68 , and one that's part of a split-diamond configuration: https://goo.gl/maps/PNwxBEWZfonJS3Ra6 .  As for dotted yield lines, the U.S. version can be found in MUTCD Figure 3B-16.  However, I'm not sure why yield lines would be used when there's a protected-only left turn signal, but they would make sense if there's a permissive phase in the signal.
"I was raised by a cup of coffee." - Strong Bad imitating Homsar

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SkyPesos

Quote from: stridentweasel on December 21, 2020, 01:57:19 PM
Quote from: SkyPesos on December 21, 2020, 01:42:34 PM
It functions like a SPUI because of the single set of signals, but also a diamond interchange because of the through movement on the ramps. Is there a name for this, tight diamond? Traffic signal order is interesting as well. On the surface road, it's the standard both lefts green first, then both straight movements green that most SPUI's use. But on the ramps, both straight movement lights turn green first, allowing the left turn vehicles to pile onto the dotted yield lines (do those even exist in the states?) under the overpass, then after both straight movement turn red, the left turns turn green. What is the name for this type of interchange, and are there any examples of this in the states? I haven't seen any examples of this outside China.
However, I'm not sure why yield lines would be used when there's a protected-only left turn signal, but they would make sense if there's a permissive phase in the signal.
I was confused about this the first time I experienced this as a roadgeek, but with the traffic signal order, it makes sense to me. The left turn yield lines are under the overpass, and when the straight movement light turns green first, the left turn vehicles can move onto the yield lines during that time (the left turn lights are still red). I guess they can fit a couple of more cars on the ramps (traffic can back up onto the expressway during rush hours constantly), or with the thought of "hey if cars have to make a really long left turn in a SPUI, why not have them do part of it while the straight movement is green, instead of waiting for the green left?". Idk what the exact reason is, but I like it. There's an example of what it looks like in my first screenshot.



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