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.

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.

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.

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.

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.

Might it be deliberate? I imagine a lot of drivers might be spooked to see "wrong" traffic, especially if it's headlights at night and they can't quite see the layout.

> When installed on a motor vehicle, the headlamps (or parts thereof) that provide the lower beam must be of the same type and provide a symmetrical effective projected luminous lens area when illuminated.

[0] https://www.federalregister.gov/documents/2022/02/22/2022-02...

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.

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

diverging diamond: https://www.openstreetmap.org/directions?engine=fossgis_osrm...

cloverleaf: https://www.openstreetmap.org/directions?engine=fossgis_osrm...

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.

NM14 is not a highway.

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...

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.

Roundabouts generally look more like this in the UK (without any overpassing roads): https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53....

Also, the motorway passes under the roundabout, not over it.

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".

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.

I’ve got older family members that have self-excluded from driving to the provincial capital because the roundabouts are overwhelming.

With right hand driving, I need to look left to consider if that traffic will be exiting or continuing. I need to look right to consider if that traffic has slowed and I need to slow. I also need to look hard left and hard right for pedestrians, who likely want to cross near the intersection (where it's most convenient) regardless of where traffic engineers are encouraging them to cross. Oh, and I better keep an eye on my mirrors, because I may need to take evasive action if the guy behind me isn't looking and I need to stop for traffic.

It's pretty hard to look at five different places at once.

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,-3.6484... . 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,-3.5975..., doing the same 4-way joining in a more transparent and forgiving way.

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,...

I'm not really saying they are scary, but they are not less scary than a roundabout IMO.

https://www.google.com/maps/@35.1052356,-106.6298892,1177m

https://www.youtube.com/watch?v=6OGvj7GZSIo

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.

Meanwhile, I've seen roundabouts that are just a circle painted in the middle of the crossing, and that's it: everybody knows how to use it. See for example the main image of the linked article below.

USA people is so against roundabouts it hurts. According to Wikipedia, there are 160 diverging diamonds in the world, 150 of them in the USA. France built two in the 1970's, and it was so good that today they have... two. Meanwhile there are at least 300 roundabouts per million of habitants in Europe (France has 1,000 per million). Heck, even the US has at least 5,000 roundabouts. Some people call them "ugly", but even they say:

"Mélanie Cathelin, who runs a toy store on one of Abbeville’s main shopping streets, said she now finds traffic lights in other cities jarring, whether in neighboring Amiens or on a recent vacation in Florida."

"To cut down on the noise, traffic jams and fender benders occurring at one intersection, Mr. Dumont decided in 2010 to turn the troublesome spot into a roundabout. It solved the problems. Ten more traffic circles followed. In October, the city’s only remaining traffic light was sawed down."

So much for an adversarial structure...

src: https://www.nytimes.com/2019/12/25/world/europe/france-round...

Strange how there are so many of them in the UK then.

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.

Here’s a YouTube video that does a much better job of highlighting these benefits. https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS

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.

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.

[1] https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac

Place de la Republique: https://www.lejdd.fr/Societe/La-place-de-la-Republique-se-re...

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

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.

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.

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.

I'm sure bridges are more expensive than roads but it seems the obvious choice versus stopping four lanes of traffic at a light.

https://de.m.wikipedia.org/wiki/Anschlussstelle_(Autobahn)#D...

That said, the intersection on average seems to be more efficient than it was before.

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.

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.

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.

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.

Still was a few incidents at the start, but the results have been dramatic.

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.

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.

https://divergingdiamond.com/history/

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...

All the other ones I've encountered are OK, lot better than roundabouts IMHO.

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 :)

It is capable flowing quite a large amount of traffic, so it's not suitable for building anywhere.

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

Not necessarily.

See here for e.g. for a large one that intersects several major roads: https://maps.app.goo.gl/51sQeVa4ozSQgW9U6?g_st=ic

Difficult, but not impossible… I’ve also used roundabouts over highway traffic, but not with the same throughput of traffic that interstates have.

They aren't really in competition with each other under most circumstances. It's like comparing bicycles and trains for transportation.

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.

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.

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.

This design seems odd to move traffic onto the wrong side of the road and make people come to a complete stop? Over-complex?

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

https://xkcd.com/2929/

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 ( coughrotarycough ) 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...

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.

The phrase "5 roundabouts in a row" is nightmare fuel for sure, but the actual map makes it look a lot more reasonable :)

I guess it's a case of "parallel discovery" - but some ~30 years later. For whatever reason, the more modern "reinvention" has taken off in a way the original did not.

[0] https://en.wikipedia.org/wiki/Diverging_diamond_interchange