I don’t know what it’s called, but there’s this wierd thing in delaware (I’ve only seen it in one place), where going left over the bridge off an offramp, you are on the “wrong” (left) side of the bridge, which is divided by barrier. There are stoplights on both end of the bridge and to get through the intersection you have to do this weird serpentine maneuver to criss-cross onto a normal configured road. It sounds like this “diverging diamond interchange”, kind of but this one is not listed in wikipedia. Its kind of in the middle of nowhere so I’m wondering if it’s a proof of concept. I don’t like it, but I admit there is a little thrill of darting diagonal across an intersection.
Note: the satellite view of this is deceptive with the tiremarks (the tiremarks betray the original traditional configuration). You can also see construction equipment so I think it was still being modified at the time. The non-satellite view is more accurate in the actual flow.
Is this it? If not, does anybody know what this is called?
Very cool. And yes, mesmerizing.
I’ve never encountered a DDI, IRL. The flow through it, for all directions, looks pretty optimal while not requiring a lot of concrete (some in Blank Slate’s video, while optimizing flow, also require a lot of land or concrete, or both).
One concern with the DDI is with its signage — will it really be clear and intuitive where you’re supposed to go? In the Wiki diagram, for example, consider a car that wants to go from the left, on US-224, and continue across I-75 and keep going to the right on US-224. At the first red fot, if there is no other traffic, instead of going straight onto the left as is the intended design it could, instead, at that first red dot, veer right and thus be thrown into oncoming traffic with the very real possibility of a head-on collision.
That could habe tragic, and possibly fatal, consequences.
As for the Silicon Valley DDI near the Apple Spaceship, that would be where Wolfe Rd crosses I-280 in Cupertino. It will be interesting to see it when it’s finished.
My wife noticed me watching that video and said, incredulously, “You’re watching traffic?” She has been laughing at me (not with me), and saying, “Why did I marry somebody so boring?” ever since.
You aren’t alone, but at such times I like to tell her that I am this way, and I don’t have much choice about how I am wired, but she had a choice and she chose to marry me.
A drive-through of a DDI as filmed from the driver’s viewpoint makes it much more clear. It’d be possible, but improbable, to make a right turn at the wrong place, but you’d have to work at it. The wrong turn would be very acute, and the arrows and signals pointing you in the right direction are obvious. I’m sure somebody might still goof up, but folks goof up and turn the wrong way on one-way streets or onto a freeway on conventional roads, too.
I’d like to see a DDI on Wolfe Road going over I-280. Once everyone is moved into Apple Park, traffic will be hellacious and they’ll need all the help they can get.
yeah, these all seem to be different takes on getting rid of traffic having to cross. any intersection design which minimizes the chance of high-speed broadside (T-bone) collisions is a good thing, IMO. when they put the SPUIs in near me (a single-diamond design) they didn’t take me much getting used to.
Yes, Apple Park will have a lot of traffic, and they will need all the help they can get! Already on I-280 the traffic builds up at the Wolfe Rd exit.
Thanks for that video, it’s helpful but it also helps to prove my point.
Imagine a tired driver driving late at night. At the beginning of the video, when the filming car stops at the red light (which is that “first red dot” I mention in post “44), imagine that there is no cross-traffic. The filming car could easily veer to the right at that light and if they did they’d be headed into oncoming traffic lanes.
Yes those lanes are marked DO NOT ENTER, but
— that right turn isn’t a sharp turn, it’s a slight veer, and
— veering right or keeping right is a natural default when driving (again, imagine the driver is tired), and it’s a natural thing to do [I have already passed the right turnoff for Provo, and I don’t want the left turnoff for Salt Lake City, so maybe veering here is what I want]
Well, maybe I’m making a mountain out of a molehill about this, but to me it’s a slight mistake that can lead to tragic if not fatal consequences.
I drive one of them occasionally. Because I don’t take it regularly, I have to think about which lane to be in each time (it’s well marked, but not as clear as I’d like until you’re “oh crap, I’m in the wrong lane”. )
Luckily, when I have to take it, it’s off-peak, so I can change lanes easily at that point when I get it wrong, which is about every 2-3 times I drive it.
If I drove it regularly, I’d have it down and it wouldn’t be a problem. Traffic does seem to flow better through there.
How well they work depends on the traffic situation. Where most the traffic is getting on the freeway, they work quite well because left turning traffic onto the freeway only needs to go through one signal instead of two. They work less well where most of the traffic doesn’t enter the freeway, since the through movements go through two signals and interfere with each other. SPUIs work well in either situation, especially if the traffic getting on and off is fairly balanced, but require a large, expensive bridge structure.
As noted above, there is one of these in the Twin Cities. While people may get used to them, this one is located on the main route into the Mall of America, as well as the route to lots of off-site airport parking. So you get lots and lots of people going through that are not regulars and have no idea what to do. It’s rather spooky, seeing ongoing traffic coming right at you.
