6 ms·

Diverging Diamond Interchange

31 points by luu 4y ago

hkwerf 4y ago
I used to love topics like this, just as I vigorously defended the construction of roundabouts. Now I have a roundabout right in front of my child's daycare. Due to the traffic rules surrounding that roundabout (Germany), it'll be impossible for him to cross that safely without me being very hands-on. All these systems are completely made to get another 2 % of efficiency for cars, while massively sacrificing walkability and bikeability. I am not a fan anymore.
- foepys 4y ago
  What rules do you mean? I have several roundabouts near me and most have prioritized pedestrian crosswalks on all exits (Zebrastreifen), some with extra room for cars to break when they notice pedestrians. The ones lacking pedestrian prioritization are outside the city or in industrial zones.
  - hkwerf 4y ago
    See my other comment. There are no Zebrastreifen on my roundabout. It's tight, heavily frequented by cars (and all sizes of trucks, due to being next to an industrial zone). Zebrastreifen would be a nice thing. However, around here it's either canonical rules for all roundabouts or even yield signs for non-car traffic. (I suppose they're only really valid for bikes which share the sidewalk, though? No idea, I just yield anyhow.) Zebrastreifen would certainly be safer than nothing. My experience, though, is, that a sufficient number of drivers is already confused or overwhelmed by basic roundabout rules and don't even see them. A traffic light simplifies everything at the cost of a bit less efficiency for cars.
- _cenw 4y ago
  I'm not sure what you mean by "traffic rules", I have a roundabout in front of my home in the middle of a major german city that's surrounded by crosswalks, with a daycare and two schools next to it.
  - hkwerf 4y ago
    It's pretty annoying: Cars have to yield to pedestrians while exiting the roundabout, they don't yield while entering. (Though luckily, many are nice enough to do anyhow.) In order to have any chance of crossing the roundabout in rush-hour traffic, I have to accept cars yielding and cross onto the middle island between exit and entry. The alternative to not crossing for yielding cars would be to wait until the roundabout is empty, which essentially never happens. However, the island is tiny. My son's bike just about fits, mine does not even fit remotely. Thus I now have to teach him to stop exactly on that island (Which, admittedly, he does very well. I don't have the confidence, though, that he'll be able to 100 % of the time. Driving past once while a car also goes by has a significant chance of causing an accident, as there is no space to evade for anybody.) This whole ordeal we have to do twice every day. It's not totally unmanagable, but a crossing with traffic lights is so much safer than these maneuvers, that include communicating and trusting cars that they know the rules as well and understand what you're about to do.
- eru 4y ago
  Not sure the roundabout is the problem? What alternative would be better? I mean adding zebra-crossing would be better, but you can combine them with a roundabout, can't you? I do agree that cars are a big problem. I wonder if we should tax them higher to properly price in their negative externalities. (And Germany already has a lot higher taxes on driving than eg the US.)
  - Dalewyn 4y ago
    >Not sure the roundabout is the problem? What alternative would be better? A simple cross intersection controlled by traffic signals. Yeah, I know I'm gonna get an imperial shit-ton of downvotes for daring to suggest traffic signals, but they are simple and involve traffic coming to a complete stop at the intersection. Simplicity is a virtue, and it's why traffic signals still reign supreme at least here in the USA.
    - omeid2 4y ago
      Roundabouts with "Raised Pedestrian Crossing" (or wombat-crossings as they're called in downunder) are pretty safe without forcing drives to wait for nothing at 3 AM. Example: https://hdp-au-prod-app-shel-letschatshellharbour-files.s3.ap-southeast-2.amazonaws.com/5916/6623/5713/4610-Shellharbour-LU-Scene_1.jpg https://hdp-au-prod-app-shel-letschatshellharbour-files.s3.a...
      - adolph 4y ago
        The only thing forcing a driver to “wait for nothing at 3am” is their own lack of pragmatic judgement. Maybe the light enforced meditation time would assist drivers like that in reëvaluating their life choices.
        omeid2 4y ago
        In Australia, there is speed and light cameras everywhere. Crossing a red light, sometimes even to make way for emergency cars, will earn you 3 demerit points, which gets you over 23% to 13 points and losing your license. Now it might not seem so dumb to wait 30 seconds, even if it is 3 AM and the road --seems empty.
- leoedin 4y ago
  In London there's been a big move over the last decade to remove big urban roundabouts for precisely that reason. They make sense for vehicles, but they make mixed use areas much more dangerous. Roundabouts are slowly being converted to C shaped junctions with dedicated cycle routes and lanes in both direction. I imagine they're probably a lot less efficient for cars, but they also don't tend to kill people at the same rate. I still think roundabouts are a great idea for more rural road junctions. They're much safer, and I suspect more efficient, than cross roads controlled by traffic lights. I was driving around Toronto last year and the amount of stopping and starting at traffic lights you have to do is infuriating.
  - jozvolskyef 4y ago
    I wonder if the distance of a pedestrian crossing from the centre of the roundabout relates to pedestrian safety. Subjectively, I feel like safety could be improved by moving the crossings farther from the centre.
    - NeoTar 4y ago
      Maybe I'm misinterpreting, but it's frustrating as a pedestrian if you ever are walking along a road and have to take a walk of even only a few metres in a perpendicular direction to find a crossing, cross, and then walk back to the original road.
      - jozvolskyef 4y ago
        It could be just five or ten meters in each direction. For example this crossing always felt unsafe to me. The original crossing has been obstructed to prevent crossings and moved about 5 meters out, and it feels much safer now: https://goo.gl/maps/ipe8RXkdSgpZz72r6 https://goo.gl/maps/ipe8RXkdSgpZz72r6
        Ekaros 4y ago
        I wonder about this specific setup for cyclist. The yield sings when coming in are after the cross walk so here in Finland in those cases the cyclist would need to yield. And even more weirdly as car is turning when going out they would need to yield on that side to cyclists. Is that same or different in Czech.
- deleted 4y ago
  [deleted]
- PartiallyTyped 4y ago
  In Denmark, pedestrians can walk in the same direction as the main flow of the road, and people who need to turn / cross the path of pedestrians yield. The priority is pedestrian > bike > car.
- alistairSH 4y ago
  Do diverging diamonds get built anyplace a person would want to walk? Around here (suburban DC,USA) they’re exclusively used where two massive highways intersect. Usually one 6+ lane interstate with a 4+ lane state highway. And the interchange itself is enormous - long, wide, noisy, stinky with fumes. Any pedestrian traffic is carried by a physically separate walking path. Not “local” sidewalks. It’s a very car-centric design. But where the highways already existed, it’s at least a traffic improvement with no reduction in pedestrian access (which was usually nil before the interchange, and improved by addition of separate walkway during construction).
  - themodelplumber 4y ago
    I usually see some not-terrible walking infrastructure around these. Though, having lived in Utah and having dined on I-5 up and down the west coast, the idea of finding oneself walking right over one, as if a car, isn't as far out there as some may believe.
  - epage 4y ago
    In Austin they are putting in diverging diamonds where regular roads intersect the interstate going through town. One of those roads in particular (Parmer Lane), they've been building out its sidewalk on the east side. So it is meant to for local pedestrian traffic except at the diverging diamond.
    - Bluestrike2 4y ago
      I was curious and looked it up on Google Maps[0] and that's definitely not a road; it's a six-lane stroad[1] optimized solely for traffic flow. Those are really good at killing pedestrians because people perceive them as being wide open, all but inviting drivers to speed up. I'm guessing the diverging diamond replaced a bridge with two intersections? In which case, the oddity of the diverging diamond might at least serve as a traffic calming measure. Even when you get used to it, switching travel directions is uncomfortable for drivers which can force them to be a bit more cautious. That said, the new sidewalks in the satellite photos are probably a big improvement over the old ones (if there were any). They at least have some small curbs and ~2-4 feet of separation from the cars traveling at high speeds along the stroad. If you look at the sidewalks to the west, where there's no separation from the stroad, they're...well, at least not that? But for the most part, sidewalks alongside stroads are just an afterthought. 0. https://goo.gl/maps/ZytZNN7TumnHqozU9 https://goo.gl/maps/ZytZNN7TumnHqozU9 1. https://en.wikipedia.org/wiki/Stroad https://en.wikipedia.org/wiki/Stroad
- kibwen 4y ago
  Thank you. Every time the roundabout discussion comes up here on HN I get dismissed when I tell people that, as a cyclist and pedestrian who does not own a car, I do everything in my power to avoid roundabouts. Please just let me cross at a junction where I can see that all cross traffic has come to a complete stop, and can make full eye contact with the drivers whose lanes I am crossing (implying nothing less than a full 90 degree intersection).
- tigeba 4y ago
  We have something that has been dubbed a "divergeabout" which is a hybrid diverging diamond intersection with roundabouts chucked on both ends. I'm pretty sure these work based entirely on fear and confusion. Fortunately this particular intersection is not really in a pedestrian area. We have roundabouts in our neighborhood and I had the same concerns about crossing when my kids were younger and walking to school.
- rented_mule 4y ago
  California's first Diverging Diamond opened a couple of years ago with a separated bicyclist/pedestrian path through the interchange[0]. It's a busy road that crosses over a busy freeway, so that path is only needed for the busy road (pedestrians and bicyclists are not supposed to use the freeway). In reality there are very few pedestrians in this area because things are _so_ spread out, but there are bicyclists. [0] https://google.com/maps/@37.783523,-121.2341659,569m/data=!3m1!1e3 https://google.com/maps/@37.783523,-121.2341659,569m/data=!3...
Moto7451 4y ago
We have these in Atlanta and while I get the concept I think they are often improperly sized and become their own form of congestion. Some of them create weaving due to lames becoming turn out on ramp lanes with little warning. It’s not uncommon to have a gridlock due to four lanes wanting to pour into two lanes. In examples where there are +1/+2 lanes where two are used for the respective on ramp/off ramp traffic there seems to be less gridlock. I didn’t grow up here so it’s possible these were built to the existing road width and the improvement was worth it even though the narrower versions are not ideally sized.
- SOLAR_FIELDS 4y ago
  They are getting pretty popular in central Texas where I live. I think they work best in a car only place where there isn’t neighborhood style traffic or pedestrians. This almost often means a location where a major road intersects a freeway. The one by the IKEA in Round Rock at 1431/I35 has been a great improvement, for example. The one on Parmer and I35 has also worked quite well. There is a similar approach, called “displaced left” down 1431 towards cedar park, however (Parmer and 1431) that has only been ok in terms of perceived improvement for traffic in the area. I will also note that they only started appearing here around 2015 onwards so maybe some design issues that you are talking about have been corrected in these newer iterations
- tbyehl 4y ago
  I have the impression the one at Pleasant Hill just isn't long enough between the lights and needs the sequencing adjusted to accommodate the incredible quantity of Atlanta-area drivers who were never taught not to block the box or that it's not a mere suggestion to stop at a red light. It has succeeded in reducing my trips to Microcenter tho.
  - Moto7451 4y ago
    Yeah, no help for me there. I used to live walking distance to the Marietta Microcenter and cam take surface streets to it now. Driving standards here are all over the place. That's a whole other issue. Atlanta has done perhaps too good of a job of attracting people who spent a long time driving in small towns where traffic is simpler.
c0nsumer 4y ago
We've a bunch of these being built in the Detroit suburbs and while I love them, the lanes on them aren't as intuitive as on a straight road, and when the roads are snow covered they can be a bit weird. I hope the road authorities keep up on line divider maintenance as well, otherwise we'll have the same problem of people drifting between lanes that snow causes. These also seem to be a bit weird for pedestrian crossings, but at least there are lights/crosswalks at all crossings as opposed to the old cloverleaf style which had nothing more than striped crossings a few feet into the highway onramp portion.
langstonzac25 4y ago
I have come across two of these in my driving career. I think it is a smart way to do a interestate exit.
coding123 4y ago
Everyone seems to be very triggered on hn topics like this as you read the comments.
- sfpotter 4y ago
  Why do you think that is?
the_gipsy 4y ago
I'd love to see that in Cities: Skylines.
- loudmax 4y ago
  You can absolutely build these in C:S and I've seen them as downloadable assets.
Gravityloss 4y ago
I saw a proposal for an oval system, ie more like an elongated stadium. No left turns. If you are coming onto this system and want to turn left, you actually turn right and go to the end where you turn around. Or if you want to leave by turning left, you first go to the end, turn around and then turn right on the way back. There are more lane changes in this system, so that's a minus. But traffic lights might not be mandatory. It would be possible to have a continuous central barrier etc.
- matzf 4y ago
  A roundabout, then?
  - Gravityloss 4y ago
    Well, it's more of a very elongated roundabout.
- dalben 4y ago
  Like this? https://www.google.com/maps/@50.8084686,3.2753331,1532m/data=!3m1!1e3 https://www.google.com/maps/@50.8084686,3.2753331,1532m/data... Known as "the Egg" locally.
- bpoyner 4y ago
  Where I live, they're proposing a Single Point Urban Interchange (SPUI) so that all interstate traffic goes through one set of traffic lights. To make that work, they have to build two flyover ramps to send the northbound traffic over the southbound traffic. https://www.penndot.pa.gov/RegionalOffices/district-11/PublicMeetings/AlleghenyCounty/Documents/I-79%20Public%20Meeting%202-07-23_rev1.pdf https://www.penndot.pa.gov/RegionalOffices/district-11/Publi...
Ancapistani 4y ago
Hey - I took the drone video in that article :) One of the very first DDIs in the country is in Springfield, MO. They’re trippy at first, but not nearly as confusing as you might think. They’re also much more efficient than I would have intuited.

31 points by luu 4y ago

I used to love topics like this, just as I vigorously defended the construction of roundabouts. Now I have a roundabout right in front of my child's daycare. Due to the traffic rules surrounding that roundabout (Germany), it'll be impossible for him to cross that safely without me being very hands-on. All these systems are completely made to get another 2 % of efficiency for cars, while massively sacrificing walkability and bikeability. I am not a fan anymore.

foepys 4y ago
What rules do you mean? I have several roundabouts near me and most have prioritized pedestrian crosswalks on all exits (Zebrastreifen), some with extra room for cars to break when they notice pedestrians. The ones lacking pedestrian prioritization are outside the city or in industrial zones.
- hkwerf 4y ago
  See my other comment. There are no Zebrastreifen on my roundabout. It's tight, heavily frequented by cars (and all sizes of trucks, due to being next to an industrial zone). Zebrastreifen would be a nice thing. However, around here it's either canonical rules for all roundabouts or even yield signs for non-car traffic. (I suppose they're only really valid for bikes which share the sidewalk, though? No idea, I just yield anyhow.) Zebrastreifen would certainly be safer than nothing. My experience, though, is, that a sufficient number of drivers is already confused or overwhelmed by basic roundabout rules and don't even see them. A traffic light simplifies everything at the cost of a bit less efficiency for cars.
_cenw 4y ago
I'm not sure what you mean by "traffic rules", I have a roundabout in front of my home in the middle of a major german city that's surrounded by crosswalks, with a daycare and two schools next to it.
- hkwerf 4y ago
  It's pretty annoying: Cars have to yield to pedestrians while exiting the roundabout, they don't yield while entering. (Though luckily, many are nice enough to do anyhow.) In order to have any chance of crossing the roundabout in rush-hour traffic, I have to accept cars yielding and cross onto the middle island between exit and entry. The alternative to not crossing for yielding cars would be to wait until the roundabout is empty, which essentially never happens. However, the island is tiny. My son's bike just about fits, mine does not even fit remotely. Thus I now have to teach him to stop exactly on that island (Which, admittedly, he does very well. I don't have the confidence, though, that he'll be able to 100 % of the time. Driving past once while a car also goes by has a significant chance of causing an accident, as there is no space to evade for anybody.) This whole ordeal we have to do twice every day. It's not totally unmanagable, but a crossing with traffic lights is so much safer than these maneuvers, that include communicating and trusting cars that they know the rules as well and understand what you're about to do.
eru 4y ago
Not sure the roundabout is the problem? What alternative would be better? I mean adding zebra-crossing would be better, but you can combine them with a roundabout, can't you? I do agree that cars are a big problem. I wonder if we should tax them higher to properly price in their negative externalities. (And Germany already has a lot higher taxes on driving than eg the US.)
- Dalewyn 4y ago
  >Not sure the roundabout is the problem? What alternative would be better? A simple cross intersection controlled by traffic signals. Yeah, I know I'm gonna get an imperial shit-ton of downvotes for daring to suggest traffic signals, but they are simple and involve traffic coming to a complete stop at the intersection. Simplicity is a virtue, and it's why traffic signals still reign supreme at least here in the USA.
  - omeid2 4y ago
    Roundabouts with "Raised Pedestrian Crossing" (or wombat-crossings as they're called in downunder) are pretty safe without forcing drives to wait for nothing at 3 AM. Example: https://hdp-au-prod-app-shel-letschatshellharbour-files.s3.ap-southeast-2.amazonaws.com/5916/6623/5713/4610-Shellharbour-LU-Scene_1.jpg https://hdp-au-prod-app-shel-letschatshellharbour-files.s3.a...
    - adolph 4y ago
      The only thing forcing a driver to “wait for nothing at 3am” is their own lack of pragmatic judgement. Maybe the light enforced meditation time would assist drivers like that in reëvaluating their life choices.
      - omeid2 4y ago
        In Australia, there is speed and light cameras everywhere. Crossing a red light, sometimes even to make way for emergency cars, will earn you 3 demerit points, which gets you over 23% to 13 points and losing your license. Now it might not seem so dumb to wait 30 seconds, even if it is 3 AM and the road --seems empty.
leoedin 4y ago
In London there's been a big move over the last decade to remove big urban roundabouts for precisely that reason. They make sense for vehicles, but they make mixed use areas much more dangerous. Roundabouts are slowly being converted to C shaped junctions with dedicated cycle routes and lanes in both direction. I imagine they're probably a lot less efficient for cars, but they also don't tend to kill people at the same rate. I still think roundabouts are a great idea for more rural road junctions. They're much safer, and I suspect more efficient, than cross roads controlled by traffic lights. I was driving around Toronto last year and the amount of stopping and starting at traffic lights you have to do is infuriating.
- jozvolskyef 4y ago
  I wonder if the distance of a pedestrian crossing from the centre of the roundabout relates to pedestrian safety. Subjectively, I feel like safety could be improved by moving the crossings farther from the centre.
  - NeoTar 4y ago
    Maybe I'm misinterpreting, but it's frustrating as a pedestrian if you ever are walking along a road and have to take a walk of even only a few metres in a perpendicular direction to find a crossing, cross, and then walk back to the original road.
    - jozvolskyef 4y ago
      It could be just five or ten meters in each direction. For example this crossing always felt unsafe to me. The original crossing has been obstructed to prevent crossings and moved about 5 meters out, and it feels much safer now: https://goo.gl/maps/ipe8RXkdSgpZz72r6 https://goo.gl/maps/ipe8RXkdSgpZz72r6
      - Ekaros 4y ago
        I wonder about this specific setup for cyclist. The yield sings when coming in are after the cross walk so here in Finland in those cases the cyclist would need to yield. And even more weirdly as car is turning when going out they would need to yield on that side to cyclists. Is that same or different in Czech.
deleted 4y ago
[deleted]
PartiallyTyped 4y ago
In Denmark, pedestrians can walk in the same direction as the main flow of the road, and people who need to turn / cross the path of pedestrians yield. The priority is pedestrian > bike > car.
alistairSH 4y ago
Do diverging diamonds get built anyplace a person would want to walk? Around here (suburban DC,USA) they’re exclusively used where two massive highways intersect. Usually one 6+ lane interstate with a 4+ lane state highway. And the interchange itself is enormous - long, wide, noisy, stinky with fumes. Any pedestrian traffic is carried by a physically separate walking path. Not “local” sidewalks. It’s a very car-centric design. But where the highways already existed, it’s at least a traffic improvement with no reduction in pedestrian access (which was usually nil before the interchange, and improved by addition of separate walkway during construction).
- themodelplumber 4y ago
  I usually see some not-terrible walking infrastructure around these. Though, having lived in Utah and having dined on I-5 up and down the west coast, the idea of finding oneself walking right over one, as if a car, isn't as far out there as some may believe.
- epage 4y ago
  In Austin they are putting in diverging diamonds where regular roads intersect the interstate going through town. One of those roads in particular (Parmer Lane), they've been building out its sidewalk on the east side. So it is meant to for local pedestrian traffic except at the diverging diamond.
  - Bluestrike2 4y ago
    I was curious and looked it up on Google Maps[0] and that's definitely not a road; it's a six-lane stroad[1] optimized solely for traffic flow. Those are really good at killing pedestrians because people perceive them as being wide open, all but inviting drivers to speed up. I'm guessing the diverging diamond replaced a bridge with two intersections? In which case, the oddity of the diverging diamond might at least serve as a traffic calming measure. Even when you get used to it, switching travel directions is uncomfortable for drivers which can force them to be a bit more cautious. That said, the new sidewalks in the satellite photos are probably a big improvement over the old ones (if there were any). They at least have some small curbs and ~2-4 feet of separation from the cars traveling at high speeds along the stroad. If you look at the sidewalks to the west, where there's no separation from the stroad, they're...well, at least not that? But for the most part, sidewalks alongside stroads are just an afterthought. 0. https://goo.gl/maps/ZytZNN7TumnHqozU9 https://goo.gl/maps/ZytZNN7TumnHqozU9 1. https://en.wikipedia.org/wiki/Stroad https://en.wikipedia.org/wiki/Stroad
kibwen 4y ago
Thank you. Every time the roundabout discussion comes up here on HN I get dismissed when I tell people that, as a cyclist and pedestrian who does not own a car, I do everything in my power to avoid roundabouts. Please just let me cross at a junction where I can see that all cross traffic has come to a complete stop, and can make full eye contact with the drivers whose lanes I am crossing (implying nothing less than a full 90 degree intersection).
tigeba 4y ago
We have something that has been dubbed a "divergeabout" which is a hybrid diverging diamond intersection with roundabouts chucked on both ends. I'm pretty sure these work based entirely on fear and confusion. Fortunately this particular intersection is not really in a pedestrian area. We have roundabouts in our neighborhood and I had the same concerns about crossing when my kids were younger and walking to school.
rented_mule 4y ago
California's first Diverging Diamond opened a couple of years ago with a separated bicyclist/pedestrian path through the interchange[0]. It's a busy road that crosses over a busy freeway, so that path is only needed for the busy road (pedestrians and bicyclists are not supposed to use the freeway). In reality there are very few pedestrians in this area because things are _so_ spread out, but there are bicyclists. [0] https://google.com/maps/@37.783523,-121.2341659,569m/data=!3m1!1e3 https://google.com/maps/@37.783523,-121.2341659,569m/data=!3...

Moto7451 4y ago

We have these in Atlanta and while I get the concept I think they are often improperly sized and become their own form of congestion. Some of them create weaving due to lames becoming turn out on ramp lanes with little warning. It’s not uncommon to have a gridlock due to four lanes wanting to pour into two lanes. In examples where there are +1/+2 lanes where two are used for the respective on ramp/off ramp traffic there seems to be less gridlock. I didn’t grow up here so it’s possible these were built to the existing road width and the improvement was worth it even though the narrower versions are not ideally sized.

SOLAR_FIELDS 4y ago
They are getting pretty popular in central Texas where I live. I think they work best in a car only place where there isn’t neighborhood style traffic or pedestrians. This almost often means a location where a major road intersects a freeway. The one by the IKEA in Round Rock at 1431/I35 has been a great improvement, for example. The one on Parmer and I35 has also worked quite well. There is a similar approach, called “displaced left” down 1431 towards cedar park, however (Parmer and 1431) that has only been ok in terms of perceived improvement for traffic in the area. I will also note that they only started appearing here around 2015 onwards so maybe some design issues that you are talking about have been corrected in these newer iterations
tbyehl 4y ago
I have the impression the one at Pleasant Hill just isn't long enough between the lights and needs the sequencing adjusted to accommodate the incredible quantity of Atlanta-area drivers who were never taught not to block the box or that it's not a mere suggestion to stop at a red light. It has succeeded in reducing my trips to Microcenter tho.
- Moto7451 4y ago
  Yeah, no help for me there. I used to live walking distance to the Marietta Microcenter and cam take surface streets to it now. Driving standards here are all over the place. That's a whole other issue. Atlanta has done perhaps too good of a job of attracting people who spent a long time driving in small towns where traffic is simpler.

c0nsumer 4y ago

We've a bunch of these being built in the Detroit suburbs and while I love them, the lanes on them aren't as intuitive as on a straight road, and when the roads are snow covered they can be a bit weird. I hope the road authorities keep up on line divider maintenance as well, otherwise we'll have the same problem of people drifting between lanes that snow causes. These also seem to be a bit weird for pedestrian crossings, but at least there are lights/crosswalks at all crossings as opposed to the old cloverleaf style which had nothing more than striped crossings a few feet into the highway onramp portion.

langstonzac25 4y ago

I have come across two of these in my driving career. I think it is a smart way to do a interestate exit.

coding123 4y ago

Everyone seems to be very triggered on hn topics like this as you read the comments.

sfpotter 4y ago
Why do you think that is?

the_gipsy 4y ago

I'd love to see that in Cities: Skylines.

loudmax 4y ago
You can absolutely build these in C:S and I've seen them as downloadable assets.

Gravityloss 4y ago

I saw a proposal for an oval system, ie more like an elongated stadium. No left turns. If you are coming onto this system and want to turn left, you actually turn right and go to the end where you turn around. Or if you want to leave by turning left, you first go to the end, turn around and then turn right on the way back. There are more lane changes in this system, so that's a minus. But traffic lights might not be mandatory. It would be possible to have a continuous central barrier etc.

matzf 4y ago
A roundabout, then?
- Gravityloss 4y ago
  Well, it's more of a very elongated roundabout.
dalben 4y ago
Like this? https://www.google.com/maps/@50.8084686,3.2753331,1532m/data=!3m1!1e3 https://www.google.com/maps/@50.8084686,3.2753331,1532m/data... Known as "the Egg" locally.
bpoyner 4y ago
Where I live, they're proposing a Single Point Urban Interchange (SPUI) so that all interstate traffic goes through one set of traffic lights. To make that work, they have to build two flyover ramps to send the northbound traffic over the southbound traffic. https://www.penndot.pa.gov/RegionalOffices/district-11/PublicMeetings/AlleghenyCounty/Documents/I-79%20Public%20Meeting%202-07-23_rev1.pdf https://www.penndot.pa.gov/RegionalOffices/district-11/Publi...

Ancapistani 4y ago

Hey - I took the drone video in that article :) One of the very first DDIs in the country is in Springfield, MO. They’re trippy at first, but not nearly as confusing as you might think. They’re also much more efficient than I would have intuited.