5 ms·

For the space that these diamond intersections use, wouldn't a roundabout also fit in that space and be a better option?

by lm2s 2y ago

PaulDavisThe1st 2y ago
Like this: https://i2-prod.examinerlive.co.uk/news/local-news/article24590136.ece/ALTERNATES/s810/0_Screen-Shot-2022-07-26-at-120410-PM.png https://i2-prod.examinerlive.co.uk/news/local-news/article24... Having said that, as someone who has some historical familiarity with these sorts of intersections, but doesn't live in a country that has them, they are pretty scary too when encountering them only rarely.
- n4r9 2y ago
  For context, that's a very specific kind of roundabout that you find near the junction of a motorway (the M1) with a primary road (the A630). The roundabout is situated on the A-road and accessed from the motorway by a slip road. That way, motorway users who don't care about the junction can just keep cruising forwards and drive over the top of the roundabout. Nevertheless, drivers can approach from any direction and exit in any direction (including back the way they came). It doesn't look like this is the case in OP's article; I'm not sure how someone approaching from the left can continue in the same direction and drive off to the right. Roundabouts generally look more like this in the UK (without any overpassing roads): https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53.3831899,-1.4611637,328m/data=!3m1!1e3!4m6!3m5!1s0x48797615634dfa59:0x32cbad1c5eccb509!8m2!3d53.4020307!4d-1.3509984!16s%2Fg%2F11cly9kj3v?entry=ttu https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53....
  - PaulDavisThe1st 2y ago
    I picked that one because it matches the sort of intersection covered in TFA. Also, the motorway passes under the roundabout, not over it.
    - n4r9 2y ago
      Oh I see! Thanks for the clarification. I think my point still stands that the motorway is not interrupted in the case of the roundabout, whilst it is in the diamond intersection.
      - PaulDavisThe1st 2y ago
        Nope, it's not :) Look at TFA again. Just like the photo I linked to, the motorway (interstate in this case) passes under the 2 bridges. The local version of this (NM14 & I25) has the interstate passing over on a single bridge, the double diamond is on the "ground level".
        n4r9 2y ago
        You're right; I hadn't scrolled down to the wide-view shot. I stand corrected.
- xattt 2y ago
  I live in a Canadian province that has enthusiastically embraced roundabouts, so I’ve been able to get used to them for years. Their efficiency is very dependent on drivers being able to anticipate the actions of others. These are things like watching the angle of the front wheels, the speed at which other cars are taking the intersection (faster = going straight through; slower = taking the turn), but also how much time it takes for a stopped car to start moving so you can judge whether you have time to enter the intersection. This is a learned skill, and not everyone in the general population has the cognitive capacity to reliably pick up on these cues. I’m not saying that I’m Nigel Mansell, but I genuinely think that the inability to pick up on these cues is why many are terrified and opposed to them.
  - PaulDavisThe1st 2y ago
    Given that countries like the UK use roundabouts incredibly extensively, and they have never been shown to be a cause of increased accident rates, I suspect that your suspicion about this is probably wrong.
    - xattt 2y ago
      It depends on the country. Familiarity with roundabouts would be a necessity in the UK. In parts of the world where roundabouts are only recent, there are many drivers who are too old to “learn new tricks”. I’ve got older family members that have self-excluded from driving to the provincial capital because the roundabouts are overwhelming.
      - PaulDavisThe1st 2y ago
        I have older friends who self-exclude from driving at night. That doesn't make me conclude that night-time driving is inherently a problem (even though it is, based on statistics, more dangerous than driving around a roundabout).
    - deleted 2y ago
      [deleted]
  - 2y ago
- otherme123 2y ago
  I find it hard to believe that the diverging diamond interchange from the link is less scary than a roundabout. Roundabouts are all the same, from the smallest (https://www.google.com/maps/@40.2258039,-3.7709757,219m/data=!3m1!1e3?entry=ttu https://www.google.com/maps/@40.2258039,-3.7709757,219m/data...) to the large (https://www.google.com/maps/@40.488386,-3.65609,436m/data=!3m1!1e3!5m1!1e1?entry=ttu https://www.google.com/maps/@40.488386,-3.65609,436m/data=!3...), unless the designer felt the need to "improve". Arrive, yield, turn right, drive until your exit, leave. Are you afraid of the inner lanes? Drive exclusively on the outer one, nobody cares. Do you need to go slower because you are in doubt? No problem, take even a second turn around if you need to get extra-sure. I need to go through 16 roundabouts everyday, and after the 1000th (2 months) you gain familiarity enough. What is this bullshit? https://www.google.com/maps/place/Madrid/@40.4965508,-3.6484745,1744m/data=!3m1!1e3!4m6!3m5!1s0xd422997800a3c81:0xc436dec1618c2269!8m2!3d40.4167754!4d-3.7037902!16zL20vMDU2X3k?entry=ttu https://www.google.com/maps/place/Madrid/@40.4965508,-3.6484... . That monstrosity, that you need to use carefully until you memorize it, is probably unique with all the mental toll that means. First time I used it, I made a bet on a lane and prayed that it went to where I wanted. A few kilometers south of that, you have this sane roundabout: https://www.google.com/maps/place/Madrid/@40.4297331,-3.5975624,873m/data=!3m1!1e3!4m6!3m5!1s0xd422997800a3c81:0xc436dec1618c2269!8m2!3d40.4167754!4d-3.7037902!16zL20vMDU2X3k?entry=ttu https://www.google.com/maps/place/Madrid/@40.4297331,-3.5975..., doing the same 4-way joining in a more transparent and forgiving way.
  - PaulDavisThe1st 2y ago
    Must the the Spanish influence :) https://www.google.com/maps/@35.1052356,-106.6298892,1177m https://www.google.com/maps/@35.1052356,-106.6298892,1177m
  - notatoad 2y ago
    >I find it hard to believe that the diverging diamond interchange from the link is less scary than a roundabout. a (good) diverging diamond is really not scary. my first time driving through one i didn't even realize i was driving through one. if you came up to this intersection, would you be able to tell you were entering a diverging diamond? or would you think it was just a normal instersection of two one-way roads? https://www.google.com/maps/@50.9043408,-114.0639993,3a,75y,43.5h,93.86t/data=!3m6!1e1!3m4!1sFyc0JyOwkRm0y1GNZqN1zQ!2e0!7i16384!8i8192?entry=ttu https://www.google.com/maps/@50.9043408,-114.0639993,3a,75y,...
- jmclnx 2y ago
  Where I am in the US, you run into them a lot. I find them easy to deal with, but I learned to drive on them. But it is funny watching non-locals deal with them and I can see why they dislike them. They work great when only people use to them drive through them.
micromacrofoot 2y ago
I think it depends on the specific traffic expectations, a roundabout interrupts the traffic flow of everything that feeds into it... the double diamond can prioritize a more uneven flow in one direction (so might be better in cases where lots of people travel in one direction, like rush hour) Might also be worth mentioning that Americans seem to be really bad at using roundabouts because they're not common in much of the country.
- nolist_policy 2y ago
  France uses roundabouts a lot and even has multi-lane roundabouts, the most famous one being around the Arc de Triomphe[1]. [1] https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac
  - bobthepanda 2y ago
    Paris under Anne Hidalgo has been undoing a lot of them because they are so hectic and pedestrian unfriendly. Place de la Republique: https://www.lejdd.fr/Societe/La-place-de-la-Republique-se-refait-321831-3111407 https://www.lejdd.fr/Societe/La-place-de-la-Republique-se-re...
    - ifwinterco 2y ago
      Same in the UK, I find it kind of funny that some North American transport planners are starting to put roundabouts everywhere at the same time as they're being ripped out in London. They're still pretty much the default junction outside of towns and cities because they do work well but large roundabouts are no fun at all to cycle round
      - bobthepanda 2y ago
        The type of roundabout being installed in America is generally one or two lanes wide, not some of the multilane monsters prevalent in the UK though.
  - deleted 2y ago
sorahn 2y ago
No. The entire point of these is to funnel the traffic onto and off the highway with out crossing any oncoming traffic, and to reduce the total number of traffic crossings overall. Here’s a YouTube video that does a much better job of highlighting these benefits. https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS
- mattlondon 2y ago
  Roundabouts don't have any traffic crossings, and sometimes don't even need traffic lights either so no one has to stop/give way
bobthepanda 2y ago
Not necessarily. Roundabouts lock up if the major flow of traffic has to go 270 degrees. (A left turn in an RHD country) Diverging diamonds do their best at handling large left turn flows since that is the type of movement that has the most reduced number of conflicts. To get any lower you would need to start building flyover ramps.

For the space that these diamond intersections use, wouldn't a roundabout also fit in that space and be a better option?

by lm2s 2y ago

For the space that these diamond intersections use, wouldn't a roundabout also fit in that space and be a better option?

PaulDavisThe1st 2y ago

Like this: https://i2-prod.examinerlive.co.uk/news/local-news/article24590136.ece/ALTERNATES/s810/0_Screen-Shot-2022-07-26-at-120410-PM.png https://i2-prod.examinerlive.co.uk/news/local-news/article24... Having said that, as someone who has some historical familiarity with these sorts of intersections, but doesn't live in a country that has them, they are pretty scary too when encountering them only rarely.

n4r9 2y ago
For context, that's a very specific kind of roundabout that you find near the junction of a motorway (the M1) with a primary road (the A630). The roundabout is situated on the A-road and accessed from the motorway by a slip road. That way, motorway users who don't care about the junction can just keep cruising forwards and drive over the top of the roundabout. Nevertheless, drivers can approach from any direction and exit in any direction (including back the way they came). It doesn't look like this is the case in OP's article; I'm not sure how someone approaching from the left can continue in the same direction and drive off to the right. Roundabouts generally look more like this in the UK (without any overpassing roads): https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53.3831899,-1.4611637,328m/data=!3m1!1e3!4m6!3m5!1s0x48797615634dfa59:0x32cbad1c5eccb509!8m2!3d53.4020307!4d-1.3509984!16s%2Fg%2F11cly9kj3v?entry=ttu https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53....
- PaulDavisThe1st 2y ago
  I picked that one because it matches the sort of intersection covered in TFA. Also, the motorway passes under the roundabout, not over it.
  - n4r9 2y ago
    Oh I see! Thanks for the clarification. I think my point still stands that the motorway is not interrupted in the case of the roundabout, whilst it is in the diamond intersection.
    - PaulDavisThe1st 2y ago
      Nope, it's not :) Look at TFA again. Just like the photo I linked to, the motorway (interstate in this case) passes under the 2 bridges. The local version of this (NM14 & I25) has the interstate passing over on a single bridge, the double diamond is on the "ground level".
      - n4r9 2y ago
        You're right; I hadn't scrolled down to the wide-view shot. I stand corrected.
xattt 2y ago
I live in a Canadian province that has enthusiastically embraced roundabouts, so I’ve been able to get used to them for years. Their efficiency is very dependent on drivers being able to anticipate the actions of others. These are things like watching the angle of the front wheels, the speed at which other cars are taking the intersection (faster = going straight through; slower = taking the turn), but also how much time it takes for a stopped car to start moving so you can judge whether you have time to enter the intersection. This is a learned skill, and not everyone in the general population has the cognitive capacity to reliably pick up on these cues. I’m not saying that I’m Nigel Mansell, but I genuinely think that the inability to pick up on these cues is why many are terrified and opposed to them.
- PaulDavisThe1st 2y ago
  Given that countries like the UK use roundabouts incredibly extensively, and they have never been shown to be a cause of increased accident rates, I suspect that your suspicion about this is probably wrong.
  - xattt 2y ago
    It depends on the country. Familiarity with roundabouts would be a necessity in the UK. In parts of the world where roundabouts are only recent, there are many drivers who are too old to “learn new tricks”. I’ve got older family members that have self-excluded from driving to the provincial capital because the roundabouts are overwhelming.
    - PaulDavisThe1st 2y ago
      I have older friends who self-exclude from driving at night. That doesn't make me conclude that night-time driving is inherently a problem (even though it is, based on statistics, more dangerous than driving around a roundabout).
  - deleted 2y ago
    [deleted]
- 2y ago
otherme123 2y ago
I find it hard to believe that the diverging diamond interchange from the link is less scary than a roundabout. Roundabouts are all the same, from the smallest (https://www.google.com/maps/@40.2258039,-3.7709757,219m/data=!3m1!1e3?entry=ttu https://www.google.com/maps/@40.2258039,-3.7709757,219m/data...) to the large (https://www.google.com/maps/@40.488386,-3.65609,436m/data=!3m1!1e3!5m1!1e1?entry=ttu https://www.google.com/maps/@40.488386,-3.65609,436m/data=!3...), unless the designer felt the need to "improve". Arrive, yield, turn right, drive until your exit, leave. Are you afraid of the inner lanes? Drive exclusively on the outer one, nobody cares. Do you need to go slower because you are in doubt? No problem, take even a second turn around if you need to get extra-sure. I need to go through 16 roundabouts everyday, and after the 1000th (2 months) you gain familiarity enough. What is this bullshit? https://www.google.com/maps/place/Madrid/@40.4965508,-3.6484745,1744m/data=!3m1!1e3!4m6!3m5!1s0xd422997800a3c81:0xc436dec1618c2269!8m2!3d40.4167754!4d-3.7037902!16zL20vMDU2X3k?entry=ttu https://www.google.com/maps/place/Madrid/@40.4965508,-3.6484... . That monstrosity, that you need to use carefully until you memorize it, is probably unique with all the mental toll that means. First time I used it, I made a bet on a lane and prayed that it went to where I wanted. A few kilometers south of that, you have this sane roundabout: https://www.google.com/maps/place/Madrid/@40.4297331,-3.5975624,873m/data=!3m1!1e3!4m6!3m5!1s0xd422997800a3c81:0xc436dec1618c2269!8m2!3d40.4167754!4d-3.7037902!16zL20vMDU2X3k?entry=ttu https://www.google.com/maps/place/Madrid/@40.4297331,-3.5975..., doing the same 4-way joining in a more transparent and forgiving way.
- PaulDavisThe1st 2y ago
  Must the the Spanish influence :) https://www.google.com/maps/@35.1052356,-106.6298892,1177m https://www.google.com/maps/@35.1052356,-106.6298892,1177m
- notatoad 2y ago
  >I find it hard to believe that the diverging diamond interchange from the link is less scary than a roundabout. a (good) diverging diamond is really not scary. my first time driving through one i didn't even realize i was driving through one. if you came up to this intersection, would you be able to tell you were entering a diverging diamond? or would you think it was just a normal instersection of two one-way roads? https://www.google.com/maps/@50.9043408,-114.0639993,3a,75y,43.5h,93.86t/data=!3m6!1e1!3m4!1sFyc0JyOwkRm0y1GNZqN1zQ!2e0!7i16384!8i8192?entry=ttu https://www.google.com/maps/@50.9043408,-114.0639993,3a,75y,...
jmclnx 2y ago
Where I am in the US, you run into them a lot. I find them easy to deal with, but I learned to drive on them. But it is funny watching non-locals deal with them and I can see why they dislike them. They work great when only people use to them drive through them.

micromacrofoot 2y ago

I think it depends on the specific traffic expectations, a roundabout interrupts the traffic flow of everything that feeds into it... the double diamond can prioritize a more uneven flow in one direction (so might be better in cases where lots of people travel in one direction, like rush hour) Might also be worth mentioning that Americans seem to be really bad at using roundabouts because they're not common in much of the country.

nolist_policy 2y ago
France uses roundabouts a lot and even has multi-lane roundabouts, the most famous one being around the Arc de Triomphe[1]. [1] https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac
- bobthepanda 2y ago
  Paris under Anne Hidalgo has been undoing a lot of them because they are so hectic and pedestrian unfriendly. Place de la Republique: https://www.lejdd.fr/Societe/La-place-de-la-Republique-se-refait-321831-3111407 https://www.lejdd.fr/Societe/La-place-de-la-Republique-se-re...
  - ifwinterco 2y ago
    Same in the UK, I find it kind of funny that some North American transport planners are starting to put roundabouts everywhere at the same time as they're being ripped out in London. They're still pretty much the default junction outside of towns and cities because they do work well but large roundabouts are no fun at all to cycle round
    - bobthepanda 2y ago
      The type of roundabout being installed in America is generally one or two lanes wide, not some of the multilane monsters prevalent in the UK though.
- deleted 2y ago

sorahn 2y ago

No. The entire point of these is to funnel the traffic onto and off the highway with out crossing any oncoming traffic, and to reduce the total number of traffic crossings overall. Here’s a YouTube video that does a much better job of highlighting these benefits. https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS

mattlondon 2y ago
Roundabouts don't have any traffic crossings, and sometimes don't even need traffic lights either so no one has to stop/give way

bobthepanda 2y ago

Not necessarily. Roundabouts lock up if the major flow of traffic has to go 270 degrees. (A left turn in an RHD country) Diverging diamonds do their best at handling large left turn flows since that is the type of movement that has the most reduced number of conflicts. To get any lower you would need to start building flyover ramps.