Why are Texas interchanges so tall?

First time I visited the US it was Houston, Texas. My host was perplexed because I laughed out loud while we were driving. Experiencing highways and those massive gas stations felt like someone had made a state that mocked America by taking prejudices we have about the American traffic and making them 200% larger in real life. My mind was blown.

It’s a shame this country is so obsessed with cars. There’s so much land yet we devote it to destroying lush ecosystems (that help reduce effects of Mother Nature) and replacing it with massive highway projects that end up costing everyone more in taxes/indefinite maintenance costs.

Then the effect is 10X’d when useless suburbs are built. More car dependence. More time spent on roads. Traffic slows to a halt as suburbs fill up. Geniuses at the state transportation department believe we should just widen the roads. But continue to ignore decades of “induced demand” evidence.

So...

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

OK, I buy that Texas has more grade-separated interchanges on average... but I'm not seeing how that turns into "Texas has more higher interchanges" which is what it feels like that question is asking. Frontage roads don't generally exist where 3+ highways intersect, so that shouldn't be relevant for high ones, it just raises many 1-high to 2-high.

Or do they, in Texas? Or is it just that Texas has one famous one and people extrapolate that to mean the whole state is absolutely smothered in interchanges, until it looks like a scene from The Fifth Element?

I heard somewhere that the reason is to provide trucks the ability to shed speed to make these sharp turns, and then give them back their speed when coming back down so they don’t have to brake hard or spend a lot of gas to do it.

Basically lets trucks use gravity to store their energy when making sharp turns and then get it back for nearly free.

"the worst symbol of our car-obsessed culture"

Nothing against the article, which covers an interesting topic. But this refrain gets tiresome, the railing against our "car obsession."

We have a big-ass country. We like to move about it. Many of us don't want or need to live on top of each other. That is all.

As somebody who lived in Dallas and drove on the high five with some frequency, I had actually a lot of questions about the design of it. If somebody who understands this could explain I’d be happy.

For one, a lot of the overpasses had two lanes. But then they merged down to one right before you got on the highway…

What’s the point in having two lanes on the overpass that merge just before you get onto the highway? There was always slow traffic because of this.

If it was me, I would always make it so that you lose equal number of lanes To the outgoing overpasses as you will get in incoming overpasses to prevent inefficient lane changes. So if you have six lanes, you get 4 branch off, 2 for each direction on the other highway and keep 2. Then you get the four back from the intersection. No lane change.

But the way they have it, there’s so much merging it , which is harder to drive, and I’m not sure it’s more efficient.

Any thoughts?

Frontage roads force a design decision. Texas likes to run the frontage roads through the interchange ramps. California generally displaces the freeway about 200m from major surface roads to avoid running the surface street through the ramps. CA-92 at US-101 does that.

When too many layers are needed, CALTRANS often goes for a tunnel underneath. See CA-92 at I-280, and SF's 19th Avenue at I-280.

At US-101 and I-280 in San Francisco, a frontage road does go through the ramps. The interchange was spread out horizontally to avoid piling up all the levels.

I lived in Dallas for a couple years, and while driving the Hive Five interchange (mentioned in the article) always seemed a little crazy, what really blew my mind was that a specific interchange could warrant its own Wikipedia page. For some reason that more than anything else really underscored its scale.

https://en.wikipedia.org/wiki/High_Five_Interchange

> 37 bridges and more than 700 columns are crammed into this one spot to keep the roughly half a million vehicles flowing in every direction each day

Truly pitiful numbers for a project of this scale lol.

i resent the default cynicism that is trendy when discussing highway infra. A clear bias against cars as ugly, dirty , polluting, etc.

This interchange provides food and prosperity to millions of people. And it's an incredible feat.

The cynical attitude is just cliche and tacky give it up.

Does anyone know why the flyover ramps in a stacked interchange usually have such large vertical clearances? The vertical separation seems much larger than necessary to accommodate the tallest trucks allowed on the highway.

EDIT: There are some more theories here:

https://engineering.stackexchange.com/questions/4238/why-are...

Obviously there may be many contributing factors, but I expect one is dominant. This one is most convincing to me: The flyover ramp generally needs to go over some things and under other things. Additionally, for both safety and rider comfort, the ramp needs to be vertically smooth, not having fast drops or rapid climbs. That means ramp A might pass over ramp B by a lot more than the minimum amount because ramp A also needs to pass over ramp C just a bit later, where it does so by a much lower amount. With many overlapping constraints like this, most ramp intersections are much higher than the minimum clearance even though none can be lowered without either (1) making one of the clearances below minimum or (2) forcing a ramp to rapidly climb/descent.

I only had a quick skim so far, but I did not feel like the article gave a firm enough rationale?

I have seen scenarios in Texas when there is seemingly no other infrastructure or geography that could explain the over building.

As cool as the engineering is, I avoid such interchanges at all costs since the being so high up gives me panic attacks when driving...

I recall seeing a regional breakdown on what different parts of the US call the frontage road. Fun fact, apparently the Houston area is the only place that uses the term "feeder road" (or just "the feeder").

In fact, being from Houston, I'm pretty sure most people wouldn't know what you meant if you said frontage road. It's that pervasive.

After browsing these comments, I would like to encourage fellow Dallasites to read László Krasznahorkai's short story "Nine Dragon Crossing", available in the collection The World Goes On. It's the most accurate thing I've read about being human amidst our freeways.

While the article complains about cars one challenge is simply the government's ability to reasonably operate transit - this includes things like keeping anti-social riders off it, keeping it quasi-pleasant to ride / safe / on time / not ruinously expensive.

I remember reading a long form article on HN about 2 years ago that was about Texas roads and highways. It wasn't from practical engineering though. Maybe it was the website of the guy who Grady briefly mentions in his video?

Okay, <rolls up sleeves> ...

From the OP:

>They say everything’s bigger in Texas

Me say:

$ echo "They say everything’s bigger in Texas" | sed 's/They/Texans/' | sed 's/bigger/biggest/'

echo ", including their egos."

We had a few great examples around Montreal when finally someone's brain kicked in and were removed and changed for better solutions - at what cost... well there's a great question.

Answer to headline: They rise so high to save some space, while keeping traffic flowing at a steady pace.

It's because they don't have earthquakes.

compensation (it's a psychological concept)

https://en.wikipedia.org/wiki/Compensation_(psychology)

> it’s kind of atrocious, right?

I can’t take an engineering article seriously when it leads in with bias-revealing invectives. Does EVERYTHING have to be politicized?

Perhaps Texas is uniquely specialized in building “up” and in a compact space due to all the oil and petrochemical industries and specialized knowledge ? This offers financial efficiency in building these stacked interchanges that might not be so cost effective elsewhere ?

I mean the less you move the cranes around the cheaper I’m sure

The same reason that the ULA launch system costs more than SpaceX.

Cronyism.

Video by that guy. Again.

Am I honestly the only one who wants to see a video of him getting punched in the face? He really needs to be punched in the face.