[HN Gopher] Road planners embrace the diverging diamond interchange
___________________________________________________________________
Road planners embrace the diverging diamond interchange
Author : frob
Score : 86 points
Date : 2024-05-28 14:25 UTC (8 hours ago)
(HTM) web link (www.npr.org)
(TXT) w3m dump (www.npr.org)
| lm2s wrote:
| For the space that these diamond intersections use, wouldn't a
| roundabout also fit in that space and be a better option?
| PaulDavisThe1st wrote:
| Like this:
|
| 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 wrote:
| 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/How
| arth+Ln,+Rotherham/@53....
| PaulDavisThe1st wrote:
| 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 wrote:
| 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.
| xattt wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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).
| otherme123 wrote:
| 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...) to the
| large (https://www.google.com/maps/@40.488386,-3.65609,436m/d
| ata=!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/Madr
| id/@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/@40.4297
| 331,-3.5975..., doing the same 4-way joining in a more
| transparent and forgiving way.
| PaulDavisThe1st wrote:
| Must the the Spanish influence :)
|
| https://www.google.com/maps/@35.1052356,-106.6298892,1177m
| notatoad wrote:
| >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
| ,...
| otherme123 wrote:
| Maybe it's that I never used one of them, so forgive me
| if I'm wrong: can I still go go the right it I missed the
| exit, and how? Can I do an U-turn and how? And finally,
| there are still traffic lights, and thus the potential to
| jump a red and t-bone someone.
|
| I'm not really saying they are scary, but they are not
| less scary than a roundabout IMO.
| tomohawk wrote:
| Most roundabouts are the same, and then there are magic
| roundabouts.
|
| https://www.youtube.com/watch?v=6OGvj7GZSIo
| echelon wrote:
| You don't have to predict other drivers on a diverging
| diamond.
|
| What you can't see from the aerial view is that the road-
| level indicators, slope, and guard rails enforce the
| diverging part. They're quite simple.
|
| Roundabouts feel adversarial. I don't like them.
| adgjlsfhk1 wrote:
| the primary problem with roundabouts is their throughout.
| the only way to raise throughout is to increase the radius
| since roundabouts with more than 2 lanes don't really work.
| roundabouts are great for low speed roads with moderate
| congestion but as the speeds and number of cars increase,
| they make less sense
| kwhitefoot wrote:
| > roundabouts with more than 2 lanes don't really work.
|
| Strange how there are so many of them in the UK then.
| jmclnx wrote:
| 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 wrote:
| 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 wrote:
| 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
| bobthepanda wrote:
| 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-re...
| ifwinterco wrote:
| 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 wrote:
| 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.
| micromacrofoot wrote:
| I've also heard that traffic is so chaotic around the Arc
| de Triomphe that insurers always assume 50-50 fault for
| accidents within it.
| sorahn wrote:
| 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
| mattlondon wrote:
| 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 wrote:
| 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.
| hexator wrote:
| The article doesn't mention the numerous downsides to pedestrians
| for diverging diamond interchanges. Four crossing points means a
| lot more conflict points and a lot more chances for death.
| bongodongobob wrote:
| Yeah, that's why it's illegal to walk on the side of highways.
| PaulDavisThe1st wrote:
| We have an intersection like this just south of Santa Fe,
| where NM14 intersects I25.
|
| NM14 is not a highway.
| ipqk wrote:
| But you may want to walk _across_ the highway which is almost
| always allowed.
| whoopdedo wrote:
| Making walking illegal is how you create the car-first
| culture that we now know the downsides of.
| bigstrat2003 wrote:
| Not everyone agrees that car-first design is a problem.
| ravetcofx wrote:
| Not everyone who smokes cigarettes agrees that they are a
| problem
| EricE wrote:
| Amen!
| IncreasePosts wrote:
| Even without car first culture, you're going to have big
| roadways meeting at some points, and it doesn't seem
| particularly smart to have pedestrians mixed in with that.
| howenterprisey wrote:
| Wouldn't the crossings themselves be safer because the cars are
| coming from fewer directions? I'd rather have four crossings,
| each with only one direction to look in, than two where I have
| to scan a whole intersection.
| notatoad wrote:
| I dunno, they seem better to me (from experience actually
| walking across [1], not just looking at pictures on the
| internet)
|
| The crossing are controlled, distances are relatively short and
| the cars are only coming from one direction. It's a couple of
| crossings to get all the way through, but they're easy
| crossings.
|
| [1] https://maps.app.goo.gl/6SwfTPrnXkUtTyym8?g_st=ic
| ipqk wrote:
| But each conflict point is crossing only one direction of
| traffic, and there are no cars turning left or right into the
| crosswalks (which is huge cause of pedestrian impacts). So even
| though there are 4 crosswalks, maybe the aggregate danger is
| less?
| bobthepanda wrote:
| It's just extremely unpleasant as a pedestrian to be in the
| middle of 55MPH (88km/h) traffic, even if you are separated
| by concrete barriers, due to all the noise and particulates.
|
| Each individual crossing is also wider if you are staying on
| the same side of the road. In a traditional diamond you'd be
| crossing one-lane on and off ramps, not half of one of the
| major roads each time.
| edward28 wrote:
| Roadguyrob has a video detailing this issue.
| https://youtube.com/watch?v=xlnz04EZpMQ
| marcinzm wrote:
| I don't see why this is unique to a divergent diamond as it
| only applies to non-light controlled points of conflict of
| which there are at most two in both designs...
| Piskvorrr wrote:
| Four crossing points (two with traffic lights, in this case),
| whereas for a "normal" interchange, you'd get...also four
| crossing points.
|
| diverging diamond:
| https://www.openstreetmap.org/directions?engine=fossgis_osrm...
|
| cloverleaf:
| https://www.openstreetmap.org/directions?engine=fossgis_osrm...
| firesteelrain wrote:
| There is one ten mins from me. It is definitely safer for
| pedestrians and bike riders. It wasn't built for golf carts
| (this is Florida) which really chaps people here. But once they
| got the lights synchronized, the design works really well.
| There are little to no accidents. We also have two traffic
| circles that people call murder circles. The main one has high
| incident of traffic accidents albeit very very minor in terms
| of damage and almost no injury.
| skywhopper wrote:
| There's actually fewer crossings involved, so safety for
| pedestrians should improve as well. But notably these
| interchanges are often in extremely pedestrian-hostile areas
| anyway, but it seems more likely that a newly constructed
| interchange will make at least some attempt to accommodate
| pedestrians, whereas interchanges built 30+ years ago often
| ignore pedestrian concerns entirely.
| aidenn0 wrote:
| This specific interchange looks superior to both a traditional
| diamond and a cloverleaf for pedestrians. All crossing points
| are controlled by a light (unlike a cloverleaf), and you don't
| have to worry about cars taking an unprotected left-turn into
| you:
|
| https://www.google.com/maps/@38.8171139,-77.6412514,3a,75y,3...
|
| [edit]
|
| The westbound on-ramp crossing appears to _not_ be protected by
| a light[1], so would be similar to a cloverleaf onramp; still
| it 's "not bad" as far as non-human-scale interchanges go.
|
| 1:
| https://www.google.com/maps/@38.8191922,-77.6383384,3a,75y,2...
| athenot wrote:
| Original title: When driving on the wrong side of the road is the
| right way to speed up traffic
|
| There are a few Diverging Diamond intersections around here and
| they seem to all work rather well from a vehicle perspective. I
| can't speak about the pedestrian side of that equation, as I've
| never been on foot.
|
| Compares to a roundabout placed over a highway, it uses 1 bridge
| instead of two, but otherwise I don't know which flows best.
| PaulDavisThe1st wrote:
| The photos in TFA show 2 bridges.
| Havoc wrote:
| And looks like they also intentionally separated them by a
| fair distance to break the "wrong side of road" sense
| edward28 wrote:
| It can also retrofit a single bridge diamond, if needed.
| athenot wrote:
| Yes, though they are close to each other (a bit too close to
| make a roundabout).
|
| All the ones around where I live are on a single bridge; but
| they usually need to widen said bridge when they convert the
| intersection.
| bradfa wrote:
| We have had one of these locally for a while now. It does seem to
| work well but since they're rare and I don't normally drive
| around that area, when I do I really need to pay attention to the
| road signs to know what's going on and where to go as it's
| definitely not intuitive.
|
| Ours seems like it was put in instead of any other option due to
| the available real estate. The diverging diamond doesn't seem to
| take up any more space than the existing roads and intersection
| did. The existing bridge work for the highway overpass didn't
| have to change afaict.
| sybercecurity wrote:
| There is one in Ohio which I encountered when visiting family.
| At first, it is confusing and weird, but I imagine you get used
| to it if you drive through it regularly.
|
| Seemed logical as it was a bridge over an interstate, so to
| make it easier for entrance/exit ramps. Still wonder how many
| accidents happened there the first month it was open.
| briffle wrote:
| They started putting in traffic circles about 10 years ago
| where I live at intersections where they didn't have enough
| traffic to need a light. it was the same thing. The first
| time people encounter them, they go a bit slow, but you get
| used to them very quickly.
| yareally wrote:
| I think we have at least 2 of them now in the Columbus area.
| shaftway wrote:
| I read about them, and then I drove through one without even
| realizing it until afterwards. The walls were high enough
| that I didn't see vehicles to my right, and the crossings
| were close enough to square that it just felt like a normal
| intersection of two one-way streets. Once I realized, I
| actually turned around to go through it again for the novelty
| and my ADHD brain flipped off and didn't notice it again. I
| had to turn around again (to continue in my original
| direction) and that's when I actually paid attention.
|
| I think people find them weird when viewed from above, but
| when you're going through them there isn't that much to them.
| If you're in the SF Bay Area and want to try one out, there's
| one in Manteca, a little more than an hour away.
| toast0 wrote:
| > Ours seems like it was put in instead of any other option due
| to the available real estate. The diverging diamond doesn't
| seem to take up any more space than the existing roads and
| intersection did. The existing bridge work for the highway
| overpass didn't have to change afaict.
|
| Yeah, this looks like it could be built pretty space
| efficiently, especially if you already had an intersection on
| each side of the bridge. I'm sure there's ways to make it use
| more space, but it seems like it wouldn't need to be a lot more
| space anyway.
| bshow wrote:
| Yeah I am gonna try this in cities skylines 2, when they fix it.
| sumtechguy wrote:
| There are a few vids of people trying it in the first cities.
| The consensious was pretty 'meh'. Cities traffic is
| 'interesting' as its priorities are not the same in real life.
| Usually a roundabout and playing with the priority tool worked
| better. In the second one the alg is very different though so
| it may help some. Getting one setup and the lights timed
| correctly would defiantly be a challenge.
| Havoc wrote:
| That's clever. They had just better be 100% on top of
| maintenance. I can see that interaction at crossover being non-
| fun with say faded markings.
| kiba wrote:
| How hard would it be to just build a pedestrian tunnel
| underneath it and avoid the problem altogether?
| tr3ntg wrote:
| In case this isn't sarcasm:
|
| 1. Based on the article, and the parent comment here, it's
| not about the pedestrians (in this case).
|
| 2. Even if it were, it'd be much more difficult. Tunnels and
| bridges must be 10x - 100x more red tape and cost than
| surface-only structures.
| Piskvorrr wrote:
| There's an interstate _underneath_ , which is the reason
| there's a complicated intersection at all. Building another
| bridge level might be safer for pedestrians, but also more
| expensive in construction and maintenance, plus now you need
| to worry about clearance. Perhaps building a footbridge over
| the interstate a bit down the road could help, but then it
| adds a detour...there's a tradeoff in each of the cases.
| everforward wrote:
| I think you would want to go over, not under. It seems easier
| to build a 30' bridge that can support foot traffic than to
| dig a 30' tunnel that needs to support semis driving over it.
|
| One thought, if there isn't a high volume of foot traffic, is
| to just the fact that these are typically paired (one to swap
| lanes, another to get them back to the "right" side). Put a
| pedestrian crossing in the middle, and you can stop traffic
| from both directions at once. Bonus points that cars are
| supposed to stop pretty far away, so pedestrians could see
| someone running the light from much farther away rather than
| having to wait til they're 15 feet away to tell they aren't
| going to stop.
| tr3ntg wrote:
| I just commented about this. We have one of these, and it's
| new, but the layers and layers of recent roadwork make it
| extremely confusing. I've seen people driving in the wrong
| lanes around the intersection. Thankfully there are plenty of
| businesses nearby (it's not a highway) so I'm sure those errors
| are corrected quickly, but it's dangerous.
|
| That said, the intersection on average seems to be more
| efficient than it was before.
| toomuchtodo wrote:
| https://en.wikipedia.org/wiki/Diverging_diamond_interchange
|
| https://divergingdiamond.com/history/
| rc_mob wrote:
| my town has one. it seems to have helped the intersection be less
| horrible
| andrewflnr wrote:
| They never show the whole interchange in the article, for some
| reason. At least in the usual design there are two crossings,
| since you need one to get you back on the right side of the road
| again.
| https://en.wikipedia.org/wiki/Diverging_diamond_interchange#...
|
| When I first encountered one in the wild (2017 in Utah I
| believe), it sure threw me off, but I navigated it fine by
| following the signs.
| KaiMagnus wrote:
| Noticed that as well. At first I wondered for how long they
| would be driving left, but then I remembered that highway
| crossings are often mirrored. An overview of the whole
| intersection would clear things up a lot.
| erkngekr wrote:
| Yeah. Maybe they sent the photographer out to take pictures but
| didn't really explain the story to them?
| Ancapistani wrote:
| I always smile a bit when this particular topic comes up on HN.
|
| The first time I saw it here, I noticed there was a lot of
| confusion about the traffic flow - so I drove to the one
| nearest me, popped up my drone, and got aerial video of a
| complete traffic cycle.
|
| It's still in the article years later. It's weird to me to
| think that random thing I did on a lark is likely to be one of
| the more durable parts of my personal legacy.
| Fauntleroy wrote:
| Thank you for recording the video. I figured the intersection
| would need a duplicate on the other end to reverse traffic
| flow back into place, and your recording helped me confirm
| that was actually the case. Seeing it in motion, it's
| actually better than I originally thought it would be.
| rconti wrote:
| What's confusing is that most of our attention gets focused on
| "whoa, weird, driving on the wrong side of the road" and not on
| what it does to the on- and off-ramps (blue in the linked
| wikipedia image).
| stouset wrote:
| They're also often _far_ less confusing than people expect them
| to be. The interchange where you cross over is generally done
| at as close to a 90 degree angle as practical, so it "feels"
| like two one-way roads crossing at an intersection rather than
| switching to drive on the wrong side of the road.
| kulor wrote:
| It looks like a roundabout (rotary) intersection would be a more
| optimal solution.
| SAI_Peregrinus wrote:
| Roundabouts are great when there's one lane in either
| direction. They start to suck once there's more than one lane,
| since the inner lanes have to cross multiple lanes when
| entering & exiting the roundabout.
| ewhanley wrote:
| There is a diverging diamond interchange across I25 in
| Cheyenne, WY, and the next exit just a couple miles south is a
| double roundabout. It's almost like WYDOT is conducting
| intersection a/b testing.
| nottorp wrote:
| > "We did see the crashes reduced somewhere in that 40 to 50%
| range, pretty much instantaneously," she said.
|
| Yeah but as far as i know that happens every time something major
| changes in local traffic rules. People pay attention for a while,
| then get used to it and accident rate raises back up. Maybe not
| to the original levels?
|
| There were those articles about a small town that removed all
| traffic lights...
| bilsbie wrote:
| We have one of these and it's awful. Everyone just waits a long
| time at each intersection.
|
| It's basically introducing a bunch of traffic lights where none
| would be needed with other designs.
|
| The truth is that the standard cloverleaf is way superior but
| they're cheaping out on land or construction costs and trying to
| pass it off a better design.
| snowwrestler wrote:
| As they say in the article, it's intended to be better than the
| pattern where people have to turn left across oncoming traffic
| to enter or exit the highway. That often also has stoplights.
|
| A cloverleaf requires more width to fit. The highway right-of-
| way may not be wide enough, or the width may have been "eaten
| up" by widening the highway. The more lanes going through, the
| less room on the sides for exit ramps.
|
| The cloverleaf doesn't need any stoplights so in theory it
| should have the best continuous throughput. However it does
| require mixing lanes, which can lock up more easily under heavy
| traffic than separated sequential exit and entry lanes.
| petsfed wrote:
| Cloverleafs also suffer a lot more when merging traffic
| becomes backed up, since there's no guarantee that the
| traffic merging on/off will be at even close to the same
| speed as the traffic that isn't merging.
|
| It turns out that engineers select different interchange
| designs based on the expected traffic patterns, and there is
| no one-size-fits-all method.
|
| As a sidebar, my dad was part of the (huge) team of engineers
| that helped implement the first few diverging diamond
| interchanges, and so its a fun reminder of him, even if I'm
| not on a road he had any hand in designing.
| Gannon6790 wrote:
| I'd be interested in the story of how these designs got
| developed, but there's not much media centered on traffic
| engineering.
| Gannon6790 wrote:
| there are a lot more conflict points in the cloverleaf, the
| diverging diamond reduces locations where a crash may happen.
| and there are a lot of busy interchanges that don't have the
| land for a full cloverleaf. it may feel very similar to the
| driver; having to wait at one light, and then the next one. but
| we have a few diverging diamonds in my area and they work way
| better handling the higher traffic volumes we're seeing with
| recent development push.
| tr3ntg wrote:
| We have one of these and it's extremely confusing. I don't drive
| the area much, but based on a few data points before and after,
| it might just have improved things.
|
| That said, I've seen folks end up driving on the wrong side of
| the road there in one of my few drive-throughs. I think ours has
| been executed poorly with not nearly as drastic curves in the
| road, and really bad painted lines due to layers and layers of
| other roadwork on top of it.
|
| I'd love to see the data. The photos in this article represent
| what seems to be a great example: obvious curves in the road,
| clear lines, plenty of space, etc.
| FireBeyond wrote:
| There is one near here I use about once a week, and they've
| gone to lengths to address many of those challenges. Every
| single lane is flagged well in advance with what it leads to
| (Interstate North, Street North, Street South, Interstate
| South), and they also have high barriers so you basically can't
| see any of the traffic the other ways as you're moving through
| it.
|
| Still was a few incidents at the start, but the results have
| been dramatic.
| everforward wrote:
| > I think ours has been executed poorly with not nearly as
| drastic curves in the road, and really bad painted lines due to
| layers and layers of other roadwork on top of it.
|
| I find the line work on these more difficult to follow than
| usual roads. The dashed, monotone, criss-crossing lines are
| somewhat difficult for my eyes to follow. I feel confident I'm
| going to the right road, but much less confident that I'm in my
| own lane than normal.
|
| I think these might be more visually obvious if the lines were
| different colors. I.e. northbound had red lines and southbound
| had blue lines (adjusted for color blindness and maybe
| overloaded meanings). I think my eyes could follow a set of
| differently colored dashed lines much better.
| jkaptur wrote:
| My town has one of these and it seems to work great. I don't love
| it as a cyclist, but the bike path just goes underneath it, so I
| absolutely never have to go through it.
| UncleEntity wrote:
| There's one of those north of Las Vegas which is probably the
| most poorly designed intersection I've ever seen. One direction
| has a stop sign for the crossover while the other way doesn't and
| if you aren't familiar with the concept it's kind of hard to
| figure out exactly what you're supposed to do.
|
| All the other ones I've encountered are OK, lot better than
| roundabouts IMHO.
| xuhu wrote:
| Is it the one at the crossing of Cheyenne Ave and Las Vegas
| Freeway ? The instant I dropped the little Maps guy in the
| middle of it and saw the street view, the "I'm in danger" meme
| started playing in my head.
| graybeardhacker wrote:
| If they used bridges instead of intersections where the roads
| cross over each other there would be no need for traffic lights
| and it would further reduce the chance of someone driving into
| oncoming traffic. The bridges could run on top of each other and
| further reduce the area needed for the interchange.
|
| I'm sure bridges are more expensive than roads but it seems the
| obvious choice versus stopping four lanes of traffic at a light.
| desert_rue wrote:
| That only makes sense if both sets of traffic don't interact.
| Most bridges over highways that have off-ramp traffic have
| traffic lights.
| throw1230 wrote:
| That is called a stack interchange, it's much larger and much
| more expensive to build and have no peds or bike access.
| dTP90pN wrote:
| The German Wikipedia has a list of such DDIs in various countries
| (primarily France since they apparently invented them in the
| 1970s):
|
| https://de.m.wikipedia.org/wiki/Anschlussstelle_(Autobahn)#D...
| jmclnx wrote:
| Looks like it takes up a lot of space, unlike the most of the US
| and Canada, where I live the roads are all small, a large road is
| two lanes with room for parking on one side, so I guess it could
| be called 3 lanes.
|
| To build these intersections you would need to tear down many
| buildings/houses. So I doubt I will ever see that where I live.
|
| I remember years ago, I once visiting a place in the middle of
| the country, I could no believe how wide just regular roads were,
| some were 3 lanes on each side. To me, that is a highway, but it
| was in a residential area.
|
| Plus those roads were very dangerous for walking and bicycling.
| It made me feel way insecure for driving.
|
| I will take my narrow, winding, intersections were multiple
| streets meet at all different angles instead of these square wide
| grid roads any day :)
| quantified wrote:
| Roundabouts take up space too. But, they have no stoplights and
| are inherently load-balancing. I'd be interested to see why
| anyone thinks these are better.
| mbreese wrote:
| The only double diamond I routinely encounter (and just
| realized that's what it was) is around an interstate
| interchange. With the scale of the interstate traffic,
| roundabouts would be difficult to use.
|
| Difficult, but not impossible... I've also used roundabouts
| over highway traffic, but not with the same throughput of
| traffic that interstates have.
| efnx wrote:
| Don't take this the wrong way, but Americans seem to have an
| issue with roundabouts. I've seen several go in around LA and
| then promptly get turned into wacky stop signs. Btw I am
| American, though I'm living in New Zealand and I prefer
| roundabouts to stop signs.
| throw1230 wrote:
| Roundabouts have low capacity
| brnt wrote:
| Hence the turbo-roundabout.
| stouset wrote:
| Good luck putting one of those on an interstate.
| hibikir wrote:
| It's a matter of max throughput. The diverging diamonds is
| great when we are talking many lanes in all directions
| anyway, like in highway interchanges. The roundabout wins
| when max throughput is not the goal, and some of its side
| properties, like some mild traffic calming and better
| interactions with pedestrians come into effect.
|
| They aren't really in competition with each other under most
| circumstances. It's like comparing bicycles and trains for
| transportation.
| nov21b wrote:
| In Spain they managed to make roundabouts with traffic
| lights. It's not uncommon but having traffic lights on small
| roundabouts can make roundabouts very hard to navigate.
| physicsguy wrote:
| Lots of roundabouts have traffic lights here in the U.K.
|
| See here for e.g. for a large one that intersects several
| major roads:
| https://maps.app.goo.gl/51sQeVa4ozSQgW9U6?g_st=ic
| toast0 wrote:
| Roundabouts are not inherently load-balancing. If you drive
| on the right, so counter-clockwise around the roundabout, and
| there's a dominant south to north flow, you won't get a fair
| share when coming from the east.
|
| East can only enter the roundabout when there's a gap, and if
| the south to north traffic is coming from an event, or a roro
| ferry, it's going to a lot of waiting. A traffic signal
| that's in event mode isn't going to give the east entrance
| much time either, but it will have some limit, most likely
| before the capacity of the ferry or the ballgame parking lot.
| stouset wrote:
| They're not better, they serve a different purpose: primarily
| for highway access from an arterial. You're not going to put
| a roundabout on your highways, and both roads can expect to
| have the highest level of demand on throughput.
| cobbzilla wrote:
| for regular roads, sure. But this diamond style is used more at
| expressway interchanges. It's especially useful in places where
| a full cloverleaf interchange would not fit.
| aiauthoritydev wrote:
| These are for land rich countries like USA and Canada as you
| have pointed out and that too for expressways, interstates etc.
| These are not meant to be build in cities.
| throw1230 wrote:
| Well, it's a service interchange it's meant to connect a
| highway to a street road, so you'll need to build it in the
| city.
| throw1230 wrote:
| All service interchanges take a lot of space. Europe has a lot
| of system and service interchanges too. DD doesn't take a lot
| more space than a regular cloverleaf, which is commonly found
| all over Europe. It is however, less flexible, as the loops in
| cloverleaf can be shaped to fit the area.
|
| It is capable flowing quite a large amount of traffic, so it's
| not suitable for building anywhere.
| FredPret wrote:
| I love the giant grid.
|
| I've seen driveways in Calgary that are wider than national
| highways in Europe.
|
| The grid has advantages:
|
| - dead easy to navigate
|
| - lots of room for proper sidewalks, not sure what you mean
| dangerous for walking. On narrow roads pedestrians end up
| walking in the road
|
| - lots of room between opposite directions of traffic
|
| - lots of room for my giant SUV
| finack wrote:
| What a colossal waste of land. We've emitted record amounts of
| CO2 this year alone (and it's only barely June), and yet we're
| still full speed ahead on cars. Anything to avoid smaller
| setbacks and bike lanes, I guess. THAT would be horrible.
| echelon wrote:
| Bikes have their time and place, but they're not the perfect
| cure all.
|
| I've been injured and unable to use a bike. I can't fathom
| being elderly or pregnant and having to bike in the rain to
| pick up groceries.
|
| Driving and cars are amazing sometimes too. Where I live I can
| drive to the mountains and the ocean. I can go hiking, camping,
| and bring my dogs with me. I can go off-road and set up my
| telescope in the rural night sky. I can haul equipment and
| furniture myself. I love the distance I can cover. It makes the
| world accessible.
| nathanaldensr wrote:
| How _dare_ you desire to or actually exercise personal
| autonomy!
| akira2501 wrote:
| > We've emitted record amounts of CO2 this year alone
|
| Per captia CO2 generation in the US has been falling steadily
| for the past 30 years and is 25% lower now than it was in the
| 1990s. Single year maximum statistics are not useful for
| generating salient policy.
|
| > and yet we're still full speed ahead on cars
|
| They are very useful devices.
|
| > Anything to avoid smaller setbacks and bike lanes, I guess
|
| It's nice to have these things but it's pointless to compromise
| other important design elements just to tick these feel good
| boxes.
| mattlondon wrote:
| Why not just use a roundabout?
|
| This design seems odd to move traffic onto the wrong side of the
| road and make people come to a complete stop? Over-complex?
| Gannon6790 wrote:
| diverging diamonds handle much larger volumes than round a
| bouts. plus they're typically useful for interstate highway
| interchanges with large collector roads, so you can't really
| expect the high speed highway traffic to slow down and maneuver
| around a circle.
| pixl97 wrote:
| large traffic flows from one direction turning left will
| dominate a roundabout blocking access for everyone else.
| Especially at rush hour, you'll get people moving bumper to
| bumper leaving a city blocking traffic in all other directions.
| I ran into this in Indiana just north of Indianapolis. They
| have a few of the suburbs with large amounts of roundabouts.
| One of them was at a large industrial complex where everyone
| evidently left at 5. I swear 15 minutes of cars left there
| turning left and stopping the rest of the traffic.
| was_a_dev wrote:
| Like all traffic infrastructure, there's variants that work
| for such situation.
|
| Roundabouts can have bypass lanes, a protected (right) turn
| that allievates that issue.
|
| In the UK you see these, and also designs where the through
| traffic bypasses the roundabout
| rqtwteye wrote:
| This will be fun in the dark and ideally rain. Suddenly you see
| lights on your right side. Happened to me in Las Vegas, NV. There
| is an exit where you are suddenly on the left side of oncoming
| traffic. First time this happened I almost had a panic attack.
| organsnyder wrote:
| The one I drive on frequently has high enough walls that you
| don't really see the other side.
| aidenn0 wrote:
| Probably not an issue here, as there is as much space between
| the two directions as between a main road and a carriage road:
| https://www.google.com/maps/@38.8174153,-77.6405252,3a,75y,3...
| enticeing wrote:
| We have many of these where I live (at least 6) and contrary to
| what seems to be the prevailing opinion here everyone I know
| prefers them to the alternatives. Sure they can be confusing upon
| first encounter, but they are noticeably way faster than the
| traditional interchanges around here.
| cheschire wrote:
| Relevant xkcd
|
| https://xkcd.com/2929/
| MikeTheGreat wrote:
| Nice article!
|
| This part got me thinking: "Chlewicki is [...] experimenting with
| some new "mutations" of the diverging diamond, as he puts it,
| combining them with roundabouts and other innovative traffic
| design."
|
| Shoreline, WA (just north of Seattle, WA) is using exactly this
| to revise a highway overpass. They're putting in a roundabout (
| _cough_ rotary _cough_ ) on either side of I-5 [1]
|
| [1] https://engage.shorelinewa.gov/145corridor - scroll down to
| the first image in the article.
|
| I was kinda wondering where they got the idea from :)
|
| [2] Direct link to image: https://s3-us-west-1.amazonaws.com/ehq-
| production-us-califor...
| cowboysauce wrote:
| > I was kinda wondering where they got the idea from :)
|
| Parts of the country have been using roundabouts in highway
| interchanges for years. Western Colorado has a number of them.
|
| This one is close to 20 years old:
| https://www.google.com/maps/place/39%C2%B037'37.8%22N+106%C2...
|
| Another one that is basically five roundabouts in a row:
| https://www.google.com/maps/place/39%C2%B038'12.9%22N+106%C2...
|
| I know of at least two others along that same stretch of
| highway.
| Lance_ET_Compte wrote:
| God forbid a bicyclist needs to traverse this hell ...
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