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So... > Q: Why are Texas interchanges so tall? > > Frontage roads need grade separation, adding a layer. > Texas has lots of frontage roads. O

• missingcolours 2y ago
  There are frontage roads at most freeway interchanges in Texas. 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.
  • mikepurvis 2y ago
    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.
    • seijiotsu 2y ago
      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.
    • dylan604 2y ago
      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
      • mikepurvis 2y ago
        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.
        • dylan604 2y ago
          You must have skimmed over the "graphic animations" too which implies the source video from which the text was just transcribed
      • pc86 2y ago
        The "T" in TFA stands for "The" so this is sort of like saying "ATM machine."
        • dylan604 2y ago
          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.
          • pc86 2y ago
            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?
    • toast0 2y ago
      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.
    • deleted 2y ago
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    • mrguyorama 2y ago
      >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.
      • vel0city 2y ago
        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.
        • s1artibartfast 2y ago
          How utterly sane.
      • lukevp 2y ago
        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.
    • bobthepanda 2y ago
      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.
    • jcranmer 2y ago
      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.
      • s1artibartfast 2y ago
        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.
    • Sohcahtoa82 2y ago
      The gain isn't "modest". 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.
  • jcranmer 2y ago
    Frontage roads don't necessitate a lot of extra levels. Take the Circle Interchange in Chicago: https://en.wikipedia.org/wiki/Jane_Byrne_Interchange https://en.wikipedia.org/wiki/Jane_Byrne_Interchange 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).
    • mrkstu 2y ago
      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.
  • hnburnsy 2y ago
    Does HOV lanes add a level? Saw these in Arizona and always wondered how much expense the separate HOV flyovers added to the interchange cost.
    • jtriangle 2y ago
      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.
• reaperducer 2y ago
  Frontage roads don't generally exist where 3+ highways intersect… Or do they, in Texas? I've lived in several states where frontage roads are common (under various names), and Texas was the place where they were most plentiful. Older interchanges tended to run the frontage roads below grade to make them cheaper. But more recent ones tend to keep everything above grade due to flooding. Or is it just that Texas has one famous one and people extrapolate that to mean the whole state is absolutely smothered in interchanges Texas has a crazy number of highway interchanges. This is a partial selection of highway interchanges with frontage roads just in Houston. There are probably a hundred more across the state: https://maps.apple.com/?ll=29.874104,-95.556634 https://maps.apple.com/?ll=29.874104,-95.556634 https://maps.apple.com/?ll=29.726083,-95.459588 https://maps.apple.com/?ll=29.726083,-95.459588 https://maps.apple.com/?ll=29.784165,-95.561947 https://maps.apple.com/?ll=29.784165,-95.561947 https://maps.apple.com/?ll=29.785693,-95.777690 https://maps.apple.com/?ll=29.785693,-95.777690 https://maps.apple.com/?ll=29.771646,-95.154931 https://maps.apple.com/?ll=29.771646,-95.154931 https://maps.apple.com/?ll=29.940698,-95.293735 https://maps.apple.com/?ll=29.940698,-95.293735 https://maps.apple.com/?ll=30.128100,-95.229756 https://maps.apple.com/?ll=30.128100,-95.229756 https://maps.apple.com/?ll=30.050496,-95.614099 https://maps.apple.com/?ll=30.050496,-95.614099 https://maps.apple.com/?ll=29.799694,-95.451234 https://maps.apple.com/?ll=29.799694,-95.451234
  • gnatolf 2y ago
    Maybe it's just me but I expected these links to open in the recently established apple maps web page. However, on an Android phone, Google Maps opens.
    • itishappy 2y ago
      Not just you, I expected the same, and was just as surprised to find it opens Google Maps in Chrome as well.
      • mouselett 2y ago
        Same here, it opens the Maps app on my MacBook.
• nonameiguess 2y ago
  The article kind of addresses this. Texas really does have more frontage roads than other US states. In the specific example cited in the article's headline photo, both the US 75 and I-635 have frontage roads that cross each other. They stay at ground level whereas the highways elevate. Part of the reason this specific interchange has so many levels, though, which is not addressed for some reason, is that both highways have high-occupancy express lanes that are separated from other traffic and have separate interchanges with the other highway as well as separate on-ramps and off-ramps to the frontage roads. This one is particularly bad because it's where the express lane for the US 75 starts and stops. Normally, the express lanes don't have their own dedicated exits and you have to first exit to the normal highway, but US 75 has an express lane north of I-635 but not south, so there are separate entrances and exits for it here. Thankfully, I've worked from home for years now, but back in the day, this used to feature heavily in my daily commute. My wife and I worked at the same place, so typically used the US 75 express lane where it existed, and it was a bitch. To go south, you have to get off the highway onto the frontage road and then back onto the highway.
  • Zircom 2y ago
    The 75 lane your talking about is actually an HOV lane, not an express one. And I appreciate that it exits off the highway for exactly one reason and it's that it makes it so incredibly easy for the cops to setup their checkpoints to catch single people using the HOV lane without screwing over the rest of the traffic on the highway. Love to see it.
• stetrain 2y ago
  The video shows multiple 5-level interchanges in Texas where two highways intersect along with their frontage roads, turning what would otherwise be a 4-stack into a 5-stack or 6-stack interchange.
• 101011 2y ago
  Completely random tidbit of information, in Houston (and only Houston) we call them 'feeder roads.'
  • abathur 2y ago
    Ha. My partner (who moved to Houston around middle school age) and her mom both call it the feeder, but I always assumed it was a midwest thing since mom's side of the family is all from Michigan. That said, the old Harvard Dialect survey does suggest this is fairly widespread (though definitely more common in the Houston area): http://dialect.redlog.net/staticmaps/q_99.html http://dialect.redlog.net/staticmaps/q_99.html
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• legacynl 2y ago
  I don't think there are many 3+ highway interchanges. These interchanges are designed to go in places where highways intersect. And you wouldn't design highways so that more than 2 highways intersect in a single point. If you need to connect 3 highways in a certain location, you can just pull back one of the connections and make 2 separate interchanges instead of one massive one. Apparently no other country makes local stores directly accessible from the highway so 5 layer interchanges just don't exist anywhere else. This is why Texas interchanges are the highest, because they're the only interchanges in the world with 5 layers.