US and the roundabout

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booshank
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Re: US and the roundabout

Post by booshank »

Chris5156 wrote: Sat Apr 20, 2024 21:45
Peter Freeman wrote: Sat Apr 20, 2024 08:11One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.
A lot of the very large roundabout-type junctions in New England - Massachusetts especially - are not part of the "modern roundabout" rollout in the US but come from the 1960s fad for "rotaries", which had no priority rules and were treated as fast-moving circular roadways with traffic merging as though on a freeway. Most are now converted to roundabout-type priority rules but their very large size and smooth geometry works against them.
I'm guessing Sunrise Circle in Cape Town, South Africa dates to the same sort of era (mid 20th Century) as those New England rotaries. Newer ones in SA tend to be a lot smaller. I also noticed a fair few small roundabouts in Alberta, Canada, but again none of the big, multi-lane, signalised etc things you see here.
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Re: US and the roundabout

Post by Chris5156 »

booshank wrote: Tue Apr 23, 2024 20:37
Chris5156 wrote: Sat Apr 20, 2024 21:45
Peter Freeman wrote: Sat Apr 20, 2024 08:11One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.
A lot of the very large roundabout-type junctions in New England - Massachusetts especially - are not part of the "modern roundabout" rollout in the US but come from the 1960s fad for "rotaries", which had no priority rules and were treated as fast-moving circular roadways with traffic merging as though on a freeway. Most are now converted to roundabout-type priority rules but their very large size and smooth geometry works against them.
I'm guessing Sunrise Circle in Cape Town, South Africa dates to the same sort of era (mid 20th Century) as those New England rotaries. Newer ones in SA tend to be a lot smaller. I also noticed a fair few small roundabouts in Alberta, Canada, but again none of the big, multi-lane, signalised etc things you see here.
That’s still a roundabout, just a very big one. The geometry of the entry and exit points gives it away: it has entering traffic approaching head-on and then curving as it hits the circulatory carriageway, which is done to slow traffic on the approach and make it clear you need to give way to traffic moving around the circle. On a rotary approaching traffic smoothly merges in at high speed and the approaching road has turns as wide, if not wider, than the circulatory.
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Re: US and the roundabout

Post by freebrickproductions »

Apparently the FHWA is celebrating "Roundabouts Week" this week over here in the US, and is making posts online relating to them as a result. Earlier today, they shared this image on Twitter about turbo roundabouts, which mentions that this intersection in Jacksonville, FL, was the first one in the US to be turned into a turbo roundabout. So far, only one other has been built in San Jose, CA, but apparently Kentucky is also in the process of implementing some on US 68 in Draffenville. It'll be interesting to see how quickly they begin to catch-on.

As a side note, the FHWA has a document reviewing turbo roundabouts linked in their tweet about them, but a Google search also pulled-up this document to try and help encourage the implementation of turbo roundabouts from them as well.
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Re: US and the roundabout

Post by Peter Freeman »

KeithW wrote: Thu Mar 08, 2018 19:27
Burns wrote:When I drove in California, I came across a few roundabouts but I also encountered this nasty 4-way stop in Mariposa. The rules appeared to be that you went in the order you arrived but it was often too busy to properly keep tabs on who arrived when. A roundabout would have been much nicer.
That is a terrible place to put a 4 way stop. In summer I imagine there are long queues in all directions leading to frayed tempers.
I consider the US's 4-way stop to be one of the worst intersection types.

There is the problem mentioned by Burns of keeping track of arrival order - great scppe for misunderstanding and disputes. I have experienced it.

And as mentioned by Keith - the queues. The simple fact is that the type is inherently low volume, caused by its very nature of one-at-a-tiime. I haven't actually seen bad queues because most are on small residential streets, as they should be. But they do sometimes appear on higher order roads (see Burns' example).

Use a small roundabout instead! (as they are now doing).
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Re: US and the roundabout

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I find 4 way stops work well when there is a dominant flow as everyone has an equal chance of emerging. The is the downside of roundabouts if you're trying to emerge from an entry downstream of a busy one and there is little traffic to block these vehicles. I know of too many roundabouts where some approaches have massive queues waiting to join the roundabout and others just have a trickle due to unbalanced traffic flows. Four way stops would solve this problem. I agree that it's low volume but could work over here on troublesome roundabouts where all the roads are S2.
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Re: US and the roundabout

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Truvelo wrote: Sun Oct 27, 2024 16:13 I find 4 way stops work well when there is a dominant flow as everyone has an equal chance of emerging. The is the downside of roundabouts if you're trying to emerge from an entry downstream of a busy one and there is little traffic to block these vehicles. I know of too many roundabouts where some approaches have massive queues waiting to join the roundabout and others just have a trickle due to unbalanced traffic flows. Four way stops would solve this problem. I agree that it's low volume but could work over here on troublesome roundabouts where all the roads are S2.
We have mini-roundabouts for that purpose; 4-way stops are explicitly prohibited in TSRGD because of the uncertainty over priority they cause and who would be liable in the event of a collision as well as the fact Stop signs in the UK are used where visibility is a problem, not as a traffic calming device.

I have always hated 4-way stops and think they're the worst of all worlds. They devalue Stop signs, they don't improve traffic flow or safety, and they're just a mess. If a junction has unbalanced flows to the point where it is causing routine congestion then the answer is properly designed signals and you just suck up the inconvenience of a red light at 2am.
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Re: US and the roundabout

Post by KeithW »

Bryn666 wrote: Mon Oct 28, 2024 10:15 We have mini-roundabouts for that purpose; 4-way stops are explicitly prohibited in TSRGD because of the uncertainty over priority they cause and who would be liable in the event of a collision as well as the fact Stop signs in the UK are used where visibility is a problem, not as a traffic calming device.

I have always hated 4-way stops and think they're the worst of all worlds. They devalue Stop signs, they don't improve traffic flow or safety, and they're just a mess. If a junction has unbalanced flows to the point where it is causing routine congestion then the answer is properly designed signals and you just suck up the inconvenience of a red light at 2am.
What they did on Sawmill Road in Columbus Ohio was to have overhead lights which after 10 PM defaulted to flashing amber and were supposed to be treated as a 4 way stop sign. It is one of those roads which at night time dropped to the point where East West traffic was minimal.
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Re: US and the roundabout

Post by Ruperts Trooper »

Bryn666 wrote: Mon Oct 28, 2024 10:15
Truvelo wrote: Sun Oct 27, 2024 16:13 I find 4 way stops work well when there is a dominant flow as everyone has an equal chance of emerging. The is the downside of roundabouts if you're trying to emerge from an entry downstream of a busy one and there is little traffic to block these vehicles. I know of too many roundabouts where some approaches have massive queues waiting to join the roundabout and others just have a trickle due to unbalanced traffic flows. Four way stops would solve this problem. I agree that it's low volume but could work over here on troublesome roundabouts where all the roads are S2.
We have mini-roundabouts for that purpose; 4-way stops are explicitly prohibited in TSRGD because of the uncertainty over priority they cause and who would be liable in the event of a collision as well as the fact Stop signs in the UK are used where visibility is a problem, not as a traffic calming device.

I have always hated 4-way stops and think they're the worst of all worlds. They devalue Stop signs, they don't improve traffic flow or safety, and they're just a mess. If a junction has unbalanced flows to the point where it is causing routine congestion then the answer is properly designed signals and you just suck up the inconvenience of a red light at 2am.
With modern electronics there doesn't need to be inconvenient red lights at any time - it's not exactly rocket-science to use sensors to detect vehicles approaching traffic lights from one direction while nothing from others and set the lights accordingly - but NH seems averse to fitting this technology and has fixed timing even at silly o'clock when there's little or no other traffic around.
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Re: US and the roundabout

Post by freebrickproductions »

KeithW wrote: Mon Oct 28, 2024 19:39
Bryn666 wrote: Mon Oct 28, 2024 10:15 We have mini-roundabouts for that purpose; 4-way stops are explicitly prohibited in TSRGD because of the uncertainty over priority they cause and who would be liable in the event of a collision as well as the fact Stop signs in the UK are used where visibility is a problem, not as a traffic calming device.

I have always hated 4-way stops and think they're the worst of all worlds. They devalue Stop signs, they don't improve traffic flow or safety, and they're just a mess. If a junction has unbalanced flows to the point where it is causing routine congestion then the answer is properly designed signals and you just suck up the inconvenience of a red light at 2am.
What they did on Sawmill Road in Columbus Ohio was to have overhead lights which after 10 PM defaulted to flashing amber and were supposed to be treated as a 4 way stop sign. It is one of those roads which at night time dropped to the point where East West traffic was minimal.
https://www.google.com/maps/@40.0738867 ... FQAw%3D%3D
I believe traffic signal collectors/enthusiasts often refer to that as a "night time flash". It used to be more common, but has largely started to disappear, if I recall correctly, though it can still be found if you know where/when to look, especially up in the midwest and I believe the northeast. Near me, I believe a few intersections around Madison, such as this one, do still do it though. IIRC, there were a few along US 431 in Albertville that did it as well, though I believe one of the signals that did it was recently removed entirely while the others had their controllers updated to stop doing it.

A four-way flashing yellow as you described wouldn't be allowed, however, as the MUTCD has explicitly banned such for decades at this point, so it'd either be a 4-way flashing red (treated as a 4-way stop) or where the side road is flashing red and the main road is flashing yellow.
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