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Why are Texas interchanges so tall?

practical.engineering

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Re: Why are Texas interchanges so tall?

#111

Post by kube-system »

msisk6 wrote: post #96
kube-system wrote: post #85

Earlier quoted context omitted.

> There's a few trucks hauling freight There's a lot of trucks hauling freight. The US has the largest train network in the world, it notoriously handles primarily freight, and still, more than 70% of freight in the US goes by truck. If these roads are the average urban interstate highways, then about 10%ish of the traffic is heavy truck traffic. https://www.fhwa.dot.gov/policyinformation/statistics/2020/v...

I meant there's few trucks during rush hour. Overnight it's a different story. Last month I was going down south I-35 around midnight and got stuck in construction traffic in Waco and it was about 80% trucks.

Ah, I see. That's really just another reason why a 500k vehicles/day problem shouldn't be approximated as a problem of moving 500k people only during rush hour.

Re: Why are Texas interchanges so tall?

#112

Post by yossi_peti »

pc86 wrote: post #92
xyst wrote: post #90

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 subur…

I'm not sure what you think the alternative is. The US is huge compared to any similarly developed country. Is the answer huge cities right next to thousands of square miles of untouched nature? That hasn't happened in any society on the planet. It sounds like you just want everyone to live in a city and take public transit everywhere but cities are awful for your mental health[0] and most people in the US do not wan…

If people want to live in rural areas, that's fine by me. They don't particularly contribute to the problems with car-centric infrastructure in the US. The main complaints are how most cities in the US are designed in ways that are hostile to anybody who doesn't have a car, such as:

- making it difficult to get around safely by bike

- zoning restrictions that force development to be clumped in certain areas

- underdeveloped public transport with infrequent stops and limited range

- parking space requirements that limit development

- food deserts where people have to drive long distances to get groceries

There are many places in the world that have solved these problems. I don't get why it's so inconceivable to solve them in the US.

Re: Why are Texas interchanges so tall?

#113

Post by [deleted] »

TeMPOraL wrote: post #60
0cf8612b2e1e wrote: post #28

Earlier quoted context omitted.

That sounds like tens of millions in extra infrastructure costs so as to save trucks a tiny amount of gas. It is Texas, so anything is possible.

Tens of millions in extra infrastructure costs to save a lot of trucks tiny amount of gas per ride, over many rides per year, over decades? That's literally what infrastructure is meant for.

[deleted]

Re: Why are Texas interchanges so tall?

#114

Post by vel0city »

oblio wrote: post #84
WheatMillington wrote: post #57

Earlier quoted context omitted.

>That's 1½-2½ commuter rail lines or about 3-4 subway lines. Assuming every single commuter is coming from and going to the same place, sure.

During rush hour most people are going from their homes to places of employment, which are generally highly concentrated. The "homes" part is distributed, true, but guess what, once you have a good rail network, it provides decent coverage for that (which you can complement via walkability/bikeability/scooterability :-p, which makes for more liveable environments). And "train commuter rage" is much less frequent than…

> which are generally highly concentrated.

Not in the slightest in DFW. That High 5 is going to service people coming from many dozens of square miles of suburbs to many dozens of square miles of offices. People are going to be coming from Plano, McKinney, Princeton, Wylie, Garland, Richardson, Sachse, Rowlett and heading to Addison, Northwest Dallas, Carrolton, Irving, Coppell, and Grapevine. That's just the traffic from the Northeast going to West.

It's not like most of these people in the suburbs of Dallas work in Dallas. They mostly don't, they live and work all over the Metroplex. And given its expensive to sell and buy land, people will often buy a house once and stay there even though their jobs might bounce all over the Metroplex.

Re: Why are Texas interchanges so tall?

#115

Post by lotsofpulp »

oblio wrote: post #84
WheatMillington wrote: post #57

Earlier quoted context omitted.

>That's 1½-2½ commuter rail lines or about 3-4 subway lines. Assuming every single commuter is coming from and going to the same place, sure.

During rush hour most people are going from their homes to places of employment, which are generally highly concentrated. The "homes" part is distributed, true, but guess what, once you have a good rail network, it provides decent coverage for that (which you can complement via walkability/bikeability/scooterability :-p, which makes for more liveable environments). And "train commuter rage" is much less frequent than…

> The "homes" part is distributed, true, but guess what, once you have a good rail network, it provides decent coverage for that (which you can complement via walkability/bikeability/scooterability :-p, which makes for more liveable environments).

This is incorrect due to the size of land parcels that Americans aspire to. The typical 0.1+ acre size lot makes it so people are so spread out, no public transit will ever make sense.

Re: Why are Texas interchanges so tall?

#116

Post by kube-system »

oblio wrote: post #84
WheatMillington wrote: post #57

Earlier quoted context omitted.

>That's 1½-2½ commuter rail lines or about 3-4 subway lines. Assuming every single commuter is coming from and going to the same place, sure.

During rush hour most people are going from their homes to places of employment, which are generally highly concentrated. The "homes" part is distributed, true, but guess what, once you have a good rail network, it provides decent coverage for that (which you can complement via walkability/bikeability/scooterability :-p, which makes for more liveable environments). And "train commuter rage" is much less frequent than…

> During rush hour most people are going from their homes to places of employment, which are generally highly concentrated.

That used to be true in the US. But over the past 50 years, the dominance of the automobile combined with traffic patterns (and related real estate trends) have incentivized the opposite to happen. Suburban commercial development facilitates easier parking, and quicker commutes over secondary highways rather than the traditional congested main arterials into city centers. Many cities in the US already have or are starting to "doughnut". While post-war suburbanites absolutely did commute into the city, many contemporary suburbanites live, work, and shop in surburbs.

I remember a time when shopping at an American department store meant you had to "go into the city" to a place like this:

https://i.pinimg.com/originals/dc/99/a2/dc99a2e79cac5ab0fe5f...

Now, when they want to go to a department store, many Americans drive to somewhere like this, closer to their homes:

https://s.hdnux.com/photos/01/11/60/12/19333814/3/1200x0.jpg

The same trend has also happened to many other industries across the board.

Re: Why are Texas interchanges so tall?

#117

Post by chiph »

jessriedel wrote: post #13

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…

The clearances in Texas are taller than ones I've seen in other states. The national standard is 17 feet, but Texas often uses 18 feet (5.4 meters) or more. Bridges on the East coast interstates sometimes don't even make 17 feet (they often predate many standards).

The theories I've heard as to why TXDOT does this include: they wanted sufficient clearance for mobile oil drilling rigs, military vehicles[0], "just in case", and of course, bragging rights.

You can zoom in and click on the blue dots to see clearances on major TXDOT bridges here:

https://gis-txdot.opendata.arcgis.com/datasets/0126e7969bfb4...

[0] The US interstate system wasn't really planned for use by the Department of Defense in time of war, but the bill was named "National System of Interstate and Defense Highways" to help it get passed in Congress. This isn't to say that during a national emergency, the highways couldn't be cleared of civilian traffic.

https://highways.dot.gov/highway-history/interstate-system/5...

Re: Why are Texas interchanges so tall?

#118

Post by abathur »

101011 wrote: post #97
Groxx wrote: post #3

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 sho…

Completely random tidbit of information, in Houston (and only Houston) we call them 'feeder roads.'

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

Re: Why are Texas interchanges so tall?

#119

Post by [deleted] »

bsder wrote: post #109
oblio wrote: post #86

Earlier quoted context omitted.

Self driving cars don't solve high traffic volumes. Cars just can't move enough people per hour, I think the average lane can move about 1800 cars per hour and most people don't share rides unless forced to. So that means about 1800-2500 people per hour per lane. A decent subway moves about 20 000 people per hour per line, I think. Cars are low to medium density transport, at best.

> most people don't share rides unless forced to. That wasn't true in the past. My father used to carpool with other teachers for 20+ years. I remember a lot of carpooling through the 1980s and into the mid 1990s where it fizzled out. I would suggest, however, that self-driving cars would be fine for carpooling. Most people would have no problem carpooling with a self-driving car if it always picked up the same bunch…

[deleted]

Re: Why are Texas interchanges so tall?

#120

Post by jcfrei »

xyst wrote: post #90

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 subur…

The US Highway building industry is in many ways a form of a state run social system. First of all the road construction and maintenance uses a huge amount of tax dollars and redistributes it to lower class construction site and road maintenance workers and some engineering bureaus. Secondly it gives everybody equal (highway) transportation access by continuously expanding capacity on existing roads and building new highways to growing towns on the countryside. Poorer people need to buy or rent housing far away on the countryside and highways therefore democratizes their access to the urban centers with lots of jobs.

In the specific case of Texas there's also a toll road system, however this only covers a fraction of the highways in the state and the tolls themselves don't account for all the incurred costs.

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