From a quick skim of Wikipedia, it looks like the main benefit to the stack style over a conventional 2-level cloverleaf is capacity (the left-turn leaves are generally at most one lane) and speed (left turns are direct rather than 270deg, so you don't have to slow down as much when taking them).
Still, to this layman it seems like a colossal engineering cost to build all those bridges and ramps for relatively modest gain.
Cloverleaf intersections have really poor overload behavior. They're fine in low traffic areas, but in places with high traffic, the crossing streams of traffic cause cascading backups.
Stack interchanges increase acheivable throughput because you can often build enough road to allow backups for one direction to not impinge on the other flows.
It's also easier to build effective signage so there's fewer surprise lane changes.
The TFA specifically covers this, so skimming wikipedia should have been totally unnecessary.
In fact, the TFA goes further than your wiki skim to add that the merging from the highway to the clover leaf requires slowing down on the highway while entering the highway from the clover requires accelerating. Both of these things are being done in the same piece of road. It does so with graphic animations. You'd probably enjoy the TFA
This comment is misleading; the youtube video contains these animations but "the fucking article" does not. Please, if you're going to imply criticism that the article went unread, don't mention things that are instead in a video. The url attached to this post is to an article (a transcript), not to https://www.youtube.com/watch?v=-16RFXr44fY which contains the content you're talking about.
Instead, please consider helpfully linking to the animations[1] you're talking about, so that others can find them without having to waste time listening to content they already read.
Could you refrain from making low-value posts like this? This is not any better than pointing out a grammar/spelling mistake, and just degrades the quality of the conversation. Yes, you are technically correct, but teh original meaning was clear. Your original comment isn't any more contributive to the discussion than pointing out the typo in my previous sentence. I'm not trying to start an argument, but asking you to re-consider this type of posting in the future since it is both off topic and a mild form of trolling (grammar-nazi adjacent).
do you really think anyone actually cares that my comment started with "The TFA" instead of just TFA? Your comment adds absolutely nothing to the conversation.
Do you really think the best way to react to a perfectly civil comment attempting to tell you that you're saying something wrong is to get defensive and pejorative?
Yes. Your comment adds nothing to the conversation. It's like posting on the incorrect use of your/you're there/their/they're. Mistakes in grammar happen all the time. When they happen, it is easy for the reader to see the mistake and move on. Corrective comments mean nothing in the end
Corrective comments mean nothing specifically in the case where the author has no interest in correcting their behavior in the future. I realize may fall into this case, but it isn't universal. Some people seek to improve their grammar and avoid mistakes. Pointing them out doesn't have to be viewed as an attack.
Alternative responses are as simple as "thanks" or "you are correct, of course"
They mean something to readers, though, regardless of whether the author is amenable to taking in the information or not. People learn by reading, so we all benefit by giving them correctly written material to learn from.
Wrong. It is NOT easy for some people to see the mistake. People learn to read, write, and even speak by READING. And where do people do most of their reading these days? Online.
So it is to everyone's benefit to correct spelling and grammar errors. People learning English, kids, whoever... they all benefit from seeing correct language. Lashing out against it is infantile and counterproductive.
To be honest I did read the first few paragraphs and then went looking for info about the Dallas High Five as I don't think I've even been on anything taller than ~three levels— the major highway near me is the 401 and I believe it is mostly cloverleafs other than the junction with 410 and 403, so I'm much more used to that arrangement.
Don’t forget ease and safety. With a stack interchange (and many other types), you often have plenty of time beforehand to position yourself into the correct lane. But if you are going to go through a cloverleaf you will often need to make a stressful weave into the leaf, and then back again into the highway.
At a cloverleaf, the weaving between people entering a highway from one leaf and people trying to get onto the next leaf is an utter destroyer of traffic flow, especially when you add in some human behavior, where some people are assholes and won't let people merge in front of them, even when they're trying to merge to the other lane themselves.
The biggest benefit to stack over a cloverleaf is that cloverleaves have this issue that the same lane needs to be used for offgoing traffic to decelerate and oncoming traffic to accelerate. There's a partial mitigation for cloverleaves, which is to lane segregate the ramps so that there's less pressure for traffic to have to accelerate to highway speed immediately, but stacks eliminate the issue entirely.
Driving around the bay area, it seems that 90% of traffic is caused by shared onramp-offramp lanes, or insufficient distance between them.
Many highways otherwise would have much more capacity. The telltale sign of exit issues is highways that bog down to 15mph for a couple miles, only to open up to 60+ with the same number of lanes.
Total shame and often unnecessary. I wonder how many man-years are wasted as a result.
the size is also a limiting factor for the cloverleaf; a 270 degree turn at reasonable speeds requires a lot of land cause the curve radius is so huge and you're going three quarters of the way around.
there is also the weave required between exiting off a loop and other traffic entering onto it. you could theoretically get rid of it by bridging one loop over the other but then you may as well just bridge more of it without the 270 degree turn at that point.
and there are also compromise designs like the cloverstack where only two opposite sides are the 270 loops to avoid the weaving problem.
>Still, to this layman it seems like a colossal engineering cost to build all those bridges and ramps for relatively modest gain.
IMO, maybe Texas does this because Texas gets a lot more taxes than they talk about (through high property taxes), and don't really want to spend them on anything else (like socialism!), so instead they build 10 lane highway systems for the billion cars and trucks every american should own.
One-third of the Texas DPS highway budget comes from federal sources.
Another third comes from revenues from oil & gas.
About a quarter comes from state gasoline sales tax and registration taxes.
So a little more than 90% of the funding for freeway projects in Texas comes from non-property tax sources.
But even then, a lot of the recent major highway projects in Texas had some kind of toll component to them whether that just directly be toll roads or tolled "express lane" projects which often have parts of those toll revenue backed bonds going to fund things like highway interchanges and on/off ramps for the freeways.
The vast majority of the property taxes I pay go towards the schools, the public parks, the fire/police/public service, libraries, and local roads. City+County taxes are ~0.710%, just the ISD and community college is ~1.16%. A massive chunk of those city/county taxes are roads and public service people, with a bit of parks department and other things like that thrown in.
The state gets its cut mostly by sales taxes though. 6.25% is the state sales tax, with things like groceries exempted. Cities can levy up to 2% additional, for a max rate of 8.25%. Of that 2% my city levies, half of that goes to public transit.
I think this is spot on, but also keep in mind that Texas is a state built for cars, not people. There are very few places where you can safely live and get around to the things you need, and the state is so big that it’s all very high speed highways. I was just there driving from DFW to Austin and it’s 75mph, and then drove to El Paso where it’s 80 mph most of the way. The scale of highways in TX is unmatched anywhere else I’ve been. It’s pretty incredible and sad to be there. There’s not much care for aesthetics or design of roadways. So there’s some cost that’s gotta be paid because everyone needs a car just to exist in such a big sprawly place. Very catch 22, but no going back at this point. DFW takes over 3 hours to drive acrosss, Houston 2 hours. The metro areas are massive there.
It's an interchange that's tucked into the normal street grid of Chicago, taking up about 4 city blocks total, and requiring just 3 levels of bridges to get all the traffic to their destinations. The trick is that it relies on a windmill interchange rather than a stack (so the left turns aren't crossing each other in the center), and the Congress Parkway-into-Eisenhower Expressway goes from elevated highway to sunken highway over the course of the interchange. There's even a subway line in the middle of the interchange!
I think the better explanation is that the size of highway interchanges in Texas aren't meaningfully constrained, so there's little pressure to find ways to squeeze in more compact interchanges. Furthermore, I think Texas is motivated to make its interchanges high-speed--the highways look designed for a 65/70 mph speed limit, even near the city core, whereas the Kennedy Expressway near the Circle interchange drops down to 45 mph partially to deal with the confusion of the road (there are exits 51B-J on I-90 in this stretch, yes, that many exits in a single mile of road).
That is correct. All the (recent) freeways I experienced in TX were designed to go ~75 mph as a normal speed, even interchanges/overpasses, except the actual turn. Even then the turns on the cloverleaves were capable of a much higher speed than other places.
Understand that, costs aren't linear for these sorts of things. Once you have the concrete plant, and are renting cranes, deploying a ton of falsework, etc, adding another level or two isn't as insane as it sounds.
The big thing is space required, and how much structure you actually need. Texas gets hurricanes, which are a big deal, but not nearly as big of a deal as earthquakes out in california, so, building tall things out of concrete is much more viable than most places.
The only real issue in some parts of Texas is that the water table is really close to the surface, so, if you want to build tall, you need significant amounts of footing work so it doesn't sink.
Typical stack interchange elsewhere has 4 levels: freeway 1, freeway 2, freeway 1 left turns, freeway 2 left turns. Frontage roads add 5th and occasionally 6th levels.
The other thing not mentioned is the proliferation of separate express lanes, which often have dedicated flyover ramps as well.