[HN Gopher] Why are Texas interchanges so tall?
___________________________________________________________________
Why are Texas interchanges so tall?
Author : impish9208
Score : 99 points
Date : 2024-08-20 19:04 UTC (3 hours ago)
(HTM) web link (practical.engineering)
(TXT) w3m dump (practical.engineering)
| 0cf8612b2e1e wrote:
| 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.
| missingcolours wrote:
| The tl;dr to the article is "Texas freeways have frontage
| roads, which add at least one additional level to a traditional
| stack interchange, and that makes them taller than interchanges
| in e.g. California.
|
| The broader question I've always had, that's not addressed in
| the article, is "so why do California and Texas build so many
| stack interchanges while the rest of the country mostly does
| not?"
| beowulfey wrote:
| That's an interesting thought. Are there statistics out there
| for "percentage of interchanges that are stacks"?
|
| I've lived in CA and the Northeast. I didn't get the
| impression that either region uses them preferentially.
| Certainly I see them _more_ in CA, but I feel like that is
| probably because the number of interchanges is higher, ha!
| seijiotsu wrote:
| From the article:
|
| > And the design that generally provides the most capacity,
| on the smallest footprint, (often for the highest cost), is
| the stack.
|
| This would explain why there are plenty in coastal
| California, where there are tons of people to move around and
| where space is very much at a premium.
| nonameiguess wrote:
| It's addressed. The frontage roads by any reasonable measure
| seem like an objectively stupid idea that the state largely
| regrets building so much of, but they did it because it made it
| easier to acquire the adjacent land to build the highways.
| There may not be any infrastructure or geography that would
| have made building differently any harder, but the land had
| owners and Texas is probably abnormally deferential to private
| landowners as US states go.
| msisk6 wrote:
| The frontage roads are great. If the freeway comes to a
| standstill you just cross over to the frontage road and
| continue. Doesn't matter if there's an exit or not. Everyone
| has giant 4x4 trucks so you can just exit where ever you want
| and hop on the frontage road. Eventually everyone does that
| and the frontage road gets clogged so timing is everything.
| Texas is interesting.
| Groxx wrote:
| 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?
| missingcolours wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| You must have skimmed over the "graphic animations" too
| which implies the source video from which the text was
| just transcribed
| pc86 wrote:
| The "T" in TFA stands for "The" so this is sort of like
| saying "ATM machine."
| dylan604 wrote:
| 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 wrote:
| 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?
| dylan604 wrote:
| 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
| s1artibartfast wrote:
| 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"
| tofof wrote:
| 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.
|
| 1: https://youtu.be/-16RFXr44fY?t=185
| toast0 wrote:
| 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.
| mrguyorama wrote:
| >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 wrote:
| 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 wrote:
| How utterly sane.
| bobthepanda wrote:
| 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 wrote:
| 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 wrote:
| 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.
| jcranmer wrote:
| Frontage roads don't necessitate a lot of extra levels. Take
| the Circle Interchange in Chicago:
| 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 wrote:
| 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.
| reaperducer wrote:
| _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=29.726083,-95.459588
|
| https://maps.apple.com/?ll=29.784165,-95.561947
|
| https://maps.apple.com/?ll=29.785693,-95.777690
|
| https://maps.apple.com/?ll=29.771646,-95.154931
|
| https://maps.apple.com/?ll=29.940698,-95.293735
|
| https://maps.apple.com/?ll=30.128100,-95.229756
|
| https://maps.apple.com/?ll=30.050496,-95.614099
|
| https://maps.apple.com/?ll=29.799694,-95.451234
| gnatolf wrote:
| 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 wrote:
| Not just you, I expected the same, and was just as
| surprised to find it opens Google Maps in Chrome as well.
| mouselett wrote:
| Same here, it opens the Maps app on my MacBook.
| jcranmer wrote:
| On Firefox on desktop, it just opens Google Maps webpage.
| nonameiguess wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Completely random tidbit of information, in Houston (and only
| Houston) we call them 'feeder roads.'
| abathur wrote:
| 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
| lwansbrough wrote:
| > 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.
| mschuster91 wrote:
| And now imagine that these 500k people would be served by a
| decent network of trains or even buses. That would immediately
| reduce the demand for infrastructure, simply because how much
| more efficient even a single decker bus is in passengers/m2 of
| occupied road space.
| criddell wrote:
| > more efficient
|
| Depends on what you are optimizing for.
|
| I can drive to work in 15 minutes, door-to-door. I used to
| ride the bus and sometimes I would be waiting that long just
| for the bus to appear.
|
| The other factor is weather. Not many of the bus shelters
| around me (I'm in Austin) are air conditioned. Right now it's
| 103F / 39C with a feels-like temperature of 107 / 42.
| Depending on your health, just walking around can be
| dangerous.
| sroussey wrote:
| I don't live in a place where just walking around can be
| dangerous to my health.
| dylan604 wrote:
| well, aren't you special then. what's the point of this
| comment?
| estebank wrote:
| You need to compare not against what you currently have,
| but rather what you'd have if there was political will and
| budgets comparable to what was spent on the existing car
| infrastructure. Otherwise is saying that no-one wants a
| bridge to cross a river because no-one swims across.
| criddell wrote:
| Well that's a problem. I'm not willing to pay anywhere
| near as much for public transportation as I am for a
| private vehicle and everything that goes with that.
|
| But I do think you are on the right track. I think public
| transportation in the form of buses doesn't make a lot of
| sense. But if Musk had been able to deliver on his
| promise of self-driving cars, then a giant city operated
| (or at least funded) fleet of small autonomous vehicles
| offering door-to-door service and route flexibility could
| change everything.
| oblio wrote:
| 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.
| bsder wrote:
| > 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 of people every day. If I can commute in
| 35 minutes or take a self-driving carpool for 45 because
| it stopped to pick up 3 other people from my department
| along the way, that would be fine.
| vel0city wrote:
| People got into carpooling because of the oil crises.
| Then the oil glut happened, things got cheap again, those
| carpool groups broke up, and it became uncommon again.
| yongjik wrote:
| Sounds like you experienced car vs. bus in a car-optimized
| city and liked the former, which is pretty understandable.
|
| In a bus-optimized city, you'd be saying something like
| "Sure I can drive to work in 15 minutes, but it takes 5
| minutes to park, costs $20 a day, and it's ten minutes
| walking from the parking lot to the office. Much better to
| take a bus that stops right across the street."
| Gud wrote:
| Have you been to a city(and country) with a good public
| transport system? I live in Zurich(not from here) and it
| blows my mind how convenient it is to walk 25 meters to the
| nearest tram stop and easily get to anywhere in the city.
|
| I used to think like you, that having car was a necessity,
| even freedom. Now I see it for what it is, a ball and
| chain.
| j-bos wrote:
| - The municipality of Zurich has an area of 91.88km2 -
| The Dallas Fort Worth Metroplex, urban area (excluding
| huge swaths of land where people live and presumably need
| commute from) hs an area of 4,524.44km2
|
| Numbers taken from wikipedia.
| pixl97 wrote:
| Hello, texan here. No busses would do nothing for these
| people... pretty much the entire DFW area is surrounded by
| huge areas of low density suburbs. The busineses and
| locations these people are going to covers hundreds of square
| miles.
|
| Car culture builds car cities. Once you have a car city it's
| nearly impossible to fix it... it's too big and expensive and
| low density to fix.
| morsch wrote:
| Park + ride
| oblio wrote:
| Well, there are solutions but then you get into even uglier
| politics.
|
| Allow higher density housing to be built without opposition
| (for example up zoning 1 level should be automatically
| approved: single family home can be torn down to build a
| duplex, etc). Then reduce and remove parking requirements.
|
| Once that's done density will just go up on its own and...
| cars don't scale. Traffic will absolutely murder everyone
| and they'll start demanding public transit.
|
| However this whole path is killed via NIMBY.
| vel0city wrote:
| Careful what you wish for. You have to wish the whole
| wish otherwise the monkey's paw will get you. Wishing for
| higher density without also pushing for better zoning
| policies overall will just make the traffic another level
| of pain, which is something seen in a number of cities.
| Sure, we'll then just build massive apartment complexes,
| one right next to the other. Where's the grocery store
| though? Where do these people work? Oops.
|
| I see so many new residential projects with small lots or
| apartments. That's great! But still the zoning forces
| _just housing_ , so its just homes on homes on homes for
| miles.
| dylan604 wrote:
| Now imagine you've designed said trains or buses lines. Where
| did you put them? How much money did it cost? How many people
| use them now that they are built? Please, enlighten us with
| how much better you are than those that are currently in
| place that have tried and failed.
| stetrain wrote:
| And in the video the quote about keeping traffic flowing is
| laid over footage where the traffic is nearly stopped and
| creeping through the interchange.
| pixl97 wrote:
| Before this exchange 635 was just stopped around 5pm. That is
| part of the problem is you fix one spot and it move the pinch
| point down to the next exit.
| kuschku wrote:
| Assuming the 500k people all commute between 6am-9am and
| 3pm-8pm, that means this interchange moves 160k people per
| hour.
|
| That's 11/2-21/2 commuter rail lines or about 3-4 subway lines.
|
| Such interchanges are truly a monument to stupidity.
| pixl97 wrote:
| You mean hundreds if commuter rail lines because the
| population isn't centered around dense points that make rail
| useful.
|
| We're in a catch 22 trap that will cost trillions and likely
| a century to get out of.
| WheatMillington wrote:
| >That's 11/2-21/2 commuter rail lines or about 3-4 subway
| lines.
|
| Assuming every single commuter is coming from and going to
| the same place, sure.
| panick21_ wrote:
| Tell me you don't understand how rail network work without
| telling me you don't understand how rail networks work.
| vel0city wrote:
| Preface: I don't like this architecture. I think things
| need to change. I'm just describing _what is_.
|
| These are people coming from several dozen square miles
| and dispersing into several dozen square miles, flowing
| through these chokepoints. They're commuting 40, 50, or
| more miles. You'd need these people to change several bus
| lines and several train lines. Those busses would be
| snaking through messy suburbs for them to be actually
| useful. Those neighborhoods to pick them up are sprawling
| with poor walkability and a 15 minute+ walk just to the
| major road bus stop for a lot of those people. And when
| they get off the train, they're probably going to need a
| bus to navigate the sparse fields of giant empty parking
| lots to their actual workplaces.
|
| In fact, for a certain group of people this path
| practically already has a train service. US-75 runs
| parallel to the Red/Orange line. Assuming the person
| starts from Plano to go to their office job in Las
| Colinas/Irving (a _massive_ assumption here, but
| practically best case), they won 't even need to change
| trains. Let's ignore how they get _to_ Parker Road
| station for now (Park and Ride? 15 minute walk through
| their neighborhood + same time as the park and ride?) and
| start the clock from there. They 're going to commute to
| the Microsoft offices. They need to get in by 9:00 AM. So
| they instantly warp to the Parker Road Station, hop on
| the orange line at 6:46 AM. They get to North Lake
| College station at 8:07 AM. They then wait for the 229
| bus at 8:21, take that 8 stops, hop off, walk a half a
| mile (~11min), and get there at 8:40. Nearly two hours
| and they only had to change once. And once again, that's
| instantly warping to Parker Road Station. Add another
| several minutes of drive or even more for a bus to
| connect to the train.
|
| Next, they're going to take the highways, including toll
| ways. They leave from Parker Road Station, head down
| US-75, hop on Bush Turnpike, and it is an ~30min trip on
| average.
|
| Or they want to avoid tolls. They take US-75 to 635
| (taking this High Five talked about here), and it takes
| 30 minutes to an hour.
|
| Now, _theoretically_ this should get a little bit better.
| There will be a new train line with more of an East-West
| path that would be useful here. But it 'll be a train
| change at Bush Turnpike Station, and service on this new
| Silver Line won't be great at first. Potentially a 30
| minute wait for the next train at peak times. And it'll
| still take 50ish minutes after that transfer. So you'd
| look at maybe a 5 minute train ride from Parker Road to
| Bush Turnpike, wait 15 minutes for the next train, then
| still 50 minutes. Plus the 30 minutes for the bus ride
| and walk. Over an hour and a half, magically warping to
| Parker Road immediately when the train was about to leave
| and hopefully only waiting 15 minutes for the Silver Line
| train. We'll see that it is really like when it opens in
| late 2025 (hopefully). I'm still excited for it, I'm
| looking forward to not needing to drive and park all the
| way out to the airport for travel and having another way
| to Addison Circle for things like Oktoberfest and other
| events there will be great.
|
| But this is also kind of a _best case_ of someone taking
| the train versus driving. This is assuming someone lives
| close to the train lines in Plano. Their office is one
| bus line away from the station. Tons of people live even
| further out from there. Lots of people work at places
| which would require multiple bus transfers. The train
| doesn 't even go halfway out into the sprawl, and the
| surrounding cities don't want to join DART.
|
| But honestly, it makes little sense to me to have people
| living in Fairview, McKinney, Prosper, _and Melissa_
| trying to commute to an office job in Dallas
| /Irving/Grapevine/Westlake/etc. It's insane to me, but
| people choose it.
|
| But a lot of people here just have a big aversion to
| taking transit. You're seen as an oddball to many for
| acknowledging it exists. We live right next to a bus stop
| that goes to a nice train station. My wife was looking at
| taking a job that would be immediately outside a train
| station. She looked at me like I was insane for
| suggesting she think about taking the train. I usually
| take it when I go into Dallas and people think it is
| incredible I survive. I take the bus to the city park
| with my kids and people wonder what happened to my car.
| oblio wrote:
| 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 "road rage" plus a lot more people
| die or get maimed driving a car/getting hit by a car than
| they do because of trains.
| eightysixfour wrote:
| > During rush hour most people are going from their homes
| to places of employment, which are generally highly
| concentrated.
|
| This isn't as true in Dallas as in other places. The QoL
| associated with some of these problems in Dallas is part
| of the reason I left, so you're preaching to the choir,
| but the sprawl is intense.
| bsder wrote:
| > places of employment, which are generally highly
| concentrated.
|
| This is not true and is one of the problems with getting
| mass transit to work in the US.
|
| Most of the employment in the US is now smeared across
| the city. I'll give Austin as an example.
|
| Austin employment has spaced out clumps. Downtown. The UT
| campus. The Domain (old IBM/NI area). The Arboretum. Oak
| Hill. The "new" airport.
|
| Austin housing has similar clumps, generally dictated by
| how much you earn. You're probably further out than you
| would like since the real estate in the center is
| ridiculous. So, Leander, Hutto, Garfield, or Dripping
| Springs.
|
| Now, plot the flows on a map. Note the massive pileup in
| the center as people attempt to change sectors across the
| city. Most modern cities are like this. There are not two
| or three obvious points that would get a big chunk of the
| traffic.
|
| I chose Austin, but San Diego, Pittsburgh, Nashville,
| etc. all look similar.
|
| And, the news is worse than that. The "white collar" jobs
| that could be concentrated have also been the most
| displaced by surburban office parks or by WFH. The types
| of jobs that most people are employed in (service and
| warehousing--Walmart/Amazon/FedEx/UPS/etc.) are generally
| _specifically positioned_ where real estate is cheaper
| which is almost by definition off of any mass transit
| connector.
| vel0city wrote:
| > 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.
| lotsofpulp wrote:
| > 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.
| kube-system wrote:
| > 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/dc99a2e79cac5ab0f
| e5f...
|
| 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.
| kube-system wrote:
| That's 500k _vehicles_ not 500k people.
|
| While the plurality of vehicles could be single-occupant
| passenger vehicles, a good chunk of those vehicles are
| freight, multiple-occupant passenger vehicles, and some are
| even busses.
| panick21_ wrote:
| The overwhelming majority of vehicles are single-occupant,
| specially during commute.
| msisk6 wrote:
| Being someone that has sat in a lot of traffic in Texas on
| these interchanges, the number of vehicles with more than
| one person is a rounding error.
|
| There's a few trucks hauling freight, but they try to miss
| the cities during rush hour.
| kube-system wrote:
| > 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/202
| 0/v...
| msisk6 wrote:
| 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.
| kube-system wrote:
| 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.
| massysett wrote:
| Heh, I read the numbers before your last statement and drew
| the opposite conclusion: if the interchange is moving as many
| cars as 4 subway lines, seems a bargain, especially as
| subways are expensive and have much more limited networks
| than roads.
| robotnikman wrote:
| 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...
| malshe wrote:
| Me too! I can't avoid them all the time but I slow down as much
| as I can safely (this is Texas so everyone drives at least 20
| miles over the limit) and look straight ahead.
| stevenwoo wrote:
| Normally you are either going so fast you are looking far down
| the road and not over the side or really slowly, trying to not
| rear end the car in front of you, the height is not that
| noticeable unless one is a passenger. One time I was on a
| freeway in Houston at night and suddenly sparks started flying
| down on me while I was going at normal speed - it was a truck
| that had flipped on its side in the merge lane that was above
| me and to the left and was grinding against the road and the
| guardrail at about highway speed (for a little bit), that was a
| new fear unlocked.
| jnwatson wrote:
| The first time I approached the High Five I got a pit in my
| stomach, and I'm not a particular anxious person. Its scale is
| astonishing.
| msisk6 wrote:
| You should try going over one of those on a motorcycle! Good
| thing I'm not afraid of heights.
| 486sx33 wrote:
| 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
| jessriedel wrote:
| 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.
| function_seven wrote:
| This comment was posted the same time you asked your question,
| but I think it's one decent reason:
|
| https://news.ycombinator.com/item?id=41303428
| jessriedel wrote:
| It's an interesting theory, but ChatGPT was skeptical, and I
| can't find anything on the internet that supports it.
|
| Thanks for the pointer though.
| bob1029 wrote:
| Part of it may be due to constraints of the construction
| process itself (I.e. not disrupting existing traffic)
|
| I've never seen one built all at once. It's always a bunch of
| incremental changes over time.
| gosub100 wrote:
| I'm completely guessing, but maybe to prevent harmful
| oscillations from wind currents blowing between the roads?
| jeffbee wrote:
| It's because they let the same company design and build the
| interchange and own the concrete plant. "Design-build" project
| delivery. It is the same reason why the new HSR projects in
| California have ludicrous vertical and side clearance compared
| to other countries with better/cheaper HSR.
| garaetjjte wrote:
| I don't follow, why they would increase their costs on
| purpose?
| kube-system wrote:
| No clue as to the validity of the above claim, but some
| contract types expose the customer to actual costs
| exclusively. e.g. T&M or cost-plus.
| kube-system wrote:
| > The vertical separation seems much larger than necessary to
| accommodate the tallest trucks allowed on the highway.
|
| The vertical height of things we want to send down the highway
| are also sometimes larger than the tallest trucks on the
| highway.
|
| https://bloximages.newyork1.vip.townnews.com/news-journal.co...
| chiph wrote:
| 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...
| tines wrote:
| 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.
| lagniappe wrote:
| Now THAT is some cool engineering I can get behind.
| 0cf8612b2e1e wrote:
| 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.
| sroussey wrote:
| It's Texas so you would assume they want people to waste
| gas.
| Scoundreller wrote:
| I thought they wanted to sell it to other states
|
| Never understood when major exporters of $thing would
| also specifically heavily subsidize $thing
| TeMPOraL wrote:
| Organic advertising? As in, showing prospective importers
| how cool it is to have abundance of $thing.
| dylan604 wrote:
| I've never heard of the proposed gravity assist theory in
| any discussion of these interchanges. Does it happen? Sure.
| Is it one of the reasons behind the design or just
| something that happens to also be true is the actual
| question. Pontificating on the interwebs is fun
| tines wrote:
| At https://www.fhwa.dot.gov/modiv/programs/intersta/docs/
| interc... I see the short comment
|
| > At service interchanges it is desirable to design the
| interchanges with the crossroad above the freeway due to:
|
| > - The crossroad above the freeway results in longer
| sight distances to the exit ramp and gore area.
|
| > - The crossroad above the freeway allows gravity to
| assist the operation of both accelerating vehicles (the
| on-ramp has a down-grade) and decelerating vehicles (the
| off-ramp has an up-grade). In addition, the resulting
| grades generally provide longer sight distances.
|
| But that's the main thing I can find right now.
| jnwatson wrote:
| Energy savings isn't the point though. The point is so
| that large trucks won't slow down traffic having lost a
| bunch of energy from braking to get on a cloverleaf.
| TeMPOraL wrote:
| 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.
| t-3 wrote:
| Infrastructure maintenance is far cheaper in areas without
| regular freeze/thaw cycles (like most of Texas). I wouldn't
| be surprised if almost all road spending in southern states
| went straight to highways and ignored local roads though,
| as there are a ton of dirt roads unless you are in a city
| or on the highway.
| jessriedel wrote:
| Does anyone have a link to something that supports this theory?
| tempoponet wrote:
| Another couple aspects of the high-5 not mentioned in the
| video:
|
| -it doesn't have any lane merges, you can change from one
| highway to another without merging, your bridge just becomes a
| new lane on the next road
|
| -these bridges are very long leading up to the turn, so it
| displaces a lot of traffic and shifts a lot of the lane
| changing upstream.
| msisk6 wrote:
| Those steep ramps and banked curves sure are fun when an ice
| storm comes along about once every five years.
| nabla9 wrote:
| 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.
| bravetraveler wrote:
| I grew up in Appalachia and moved to Texas as an adult. Very
| similar experience, ride-laugh and all. This place is both
| amazing and ridiculous.
| hoten wrote:
| Houston native here. I still guffaw when I see a massively
| lifted truck. Everything's bigger in Texas, including egos.
| gosub100 wrote:
| 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?
| gullywhumper wrote:
| 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
| aidenn0 wrote:
| One close to where I grew up with its own page is the
| Springfield, VA interchange[1][2]. 24 lanes wide at its widest
| point.
|
| 1: https://en.wikipedia.org/wiki/Springfield_Interchange
|
| 2: https://www.openstreetmap.org/#map=17/38.791557/-77.175887
| morsch wrote:
| Loads of interchanges have Wikipedia pages:
| https://en.m.wikipedia.org/wiki/List_of_road_interchanges_in...
|
| I think literally every interchange in Germany has got its own
| article:
| https://de.m.wikipedia.org/wiki/Kategorie:Autobahnkreuz_in_D...
| Animats wrote:
| 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.
| riffic wrote:
| compensation (it's a psychological concept)
|
| https://en.wikipedia.org/wiki/Compensation_(psychology)
| h_tbob wrote:
| 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?
| Neywiny wrote:
| There's a cities skylines YouTuber who agrees with you. He
| calls it lane math. "2 come off, 2 go on,..." I'm sure there's
| some reason the engineers do it irl, but it is funny that going
| with your approach does fix things in game.
| ajkjk wrote:
| I wonder if it's more about having room for emergency vehicles
| or for people to pull over if there's an accident without
| totally stopping traffic.
| jader201 wrote:
| My guess is the two lanes merging into one are only getting one
| lane. That is, only one lane is added after the merge, and both
| overpass lanes are merging into the one new lane.
|
| But if there are indeed being two lanes added due to the merge,
| agree that doesn't make much sense.
|
| If the former, also agree that they should've added two lanes
| instead of one. But that decision could've come down to
| physical limitations, cost, or something else.
| cornstalks wrote:
| I have no answer, but this got me thinking: is the overpass's
| road a similar physical width as the highway?
|
| I've been on some bridges that have two lanes with a very
| narrow shoulder that then then merge into a single lane (with
| wider shoulders) at the end of the bridge, with the asphalt
| width not changing too much. I've always assumed that was so
| traffic could continue flowing on the bridge should one lane
| become blocked for some reason. Off the bridge a car can pull
| off the road if there's a problem to let traffic continue
| passing. You can't really do that so much on a bridge.
|
| But I'm not a traffic/road engineer so that's just speculation
| on my part.
| xyst wrote:
| 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.
| pc86 wrote:
| 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 want to live
| in a major urban area. You can't have a huge geography and
| rural or suburban life without private vehicles.
|
| [0] https://pubmed.ncbi.nlm.nih.gov/7892359/
| yossi_peti wrote:
| 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.
| lelandbatey wrote:
| The US being huge has no bearing on the requirement that I
| have to own a car to get to work every day, or to go to the
| grocery store, or to take kids to school. I live in a more
| suburban area than I used to and having to pilot a huge
| deadly vehicle everywhere is vastly more stressful than just
| _walking_ to handle my groceries.
|
| Note that the study you link to there is from 1994 and only
| controlled for the following criteria: sex, age, social
| class, marital status, unemployment, chronic illness and
| region of residence. Those aren't the things that put folks
| on edge about cities in 1994 or in the preceding years. 30
| years on from 1994 and now in a different world, many of us
| are wondering why we're locked out of some of the benefits of
| a bit more density.
|
| No ones saying we abandon all beyond our city walls to
| nature, instead they'll be farmland or productive rural
| activities like we already use them for. But we don't need
| every city of 500k people to mean that there's a 15 mile
| radius circle of strip malls in every direction.
| rbetts wrote:
| The US is large - but roughly 1 in 10 residents live around
| LA or NYC. As much as it is large, it is also non-uniform.
| jcfrei wrote:
| 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.
| consp wrote:
| Poor people should not have to buy a car as it is a massive
| drain on finances to keep it running. There are better
| solutions
| jcfrei wrote:
| Theoretically yes but a lot would need to change for that
| to happen in the US. In reality having a car and traveling
| lots of miles every day is the cheapest variant for most
| people.
| aj7 wrote:
| The same reason that the ULA launch system costs more than
| SpaceX.
|
| Cronyism.
| brcmthrowaway wrote:
| I hate Texas and anything to do with Texas.
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