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Comment by jmclnx | Hacker News Reader

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 :)

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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.

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.

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.

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.

https://maps.app.goo.gl/DEFdtvFKev54LW5M7

Not necessarily.

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.

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.

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.

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.

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

To be pedantic; roundabouts are a subset of traffic circles that don't have traffic lights or other flow control in them. Don't think I'd ever seen the term "traffic circle" until I learned that distinction though.

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.

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.

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.

Roundabouts have low capacity

Hence the turbo-roundabout.

Good luck putting one of those on an interstate.

The diverging diamond is also not _on_ the interstate, but over.

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

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