3 ms·

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 2y ago
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 2y ago
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.
- deleted 2y ago
  [deleted]
throw1230 2y ago
Roundabouts have low capacity
- brnt 2y ago
  Hence the turbo-roundabout.
  - stouset 2y ago
    Good luck putting one of those on an interstate.
    - brnt 2y ago
      The diverging diamond is also not _on_ the interstate, but over.
hibikir 2y ago
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 2y ago
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 2y ago
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 https://maps.app.goo.gl/51sQeVa4ozSQgW9U6?g_st=ic
- jimbobthrowawy 2y ago
  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.
toast0 2y ago
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 2y ago
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.

mbreese 2y ago

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 2y ago

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.

deleted 2y ago
[deleted]

throw1230 2y ago

Roundabouts have low capacity

brnt 2y ago
Hence the turbo-roundabout.
- stouset 2y ago
  Good luck putting one of those on an interstate.
  - brnt 2y ago
    The diverging diamond is also not _on_ the interstate, but over.

hibikir 2y ago

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 2y ago

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 2y ago

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 https://maps.app.goo.gl/51sQeVa4ozSQgW9U6?g_st=ic

jimbobthrowawy 2y ago
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.

toast0 2y ago

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 2y ago

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.