US and the roundabout

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bothar
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Re: US and the roundabout

Post by bothar »

Osthagen wrote:
Bryn666 wrote: Massachussetts has some grade separated rotaries, which frighten the bejeezus out of non-locals. There are several on I-95/93 around south Boston.
I drove the full I-95, including the Massachusetts section just under two years ago. It’s strange I didn’t notice these junctions. Have they been there a very long time?
Some junctions is Massachusetts look very familiar in design, not always on the Interstates but on US-1 MA-2 etc, for instance here.
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Re: US and the roundabout

Post by Peter Freeman »

Bryn666 wrote:To really upset Peter Freeman though, here is a bona fide 3 level roundabout in New Orleans: https://goo.gl/maps/EEbxa9qa3zx
Oh, how disappointing! It looks rather old (which itself is surprising), somewhat delapidated and ugly, and (at Streetview time anyway) deserted. I wonder whether it's the USA's only one - here's hoping.

However, upsetting me even more is the fact that a new freeway scheme in Perth, Western Australia, is about to build (what I believe is) AU's first stackabout :( .
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Re: US and the roundabout

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I've heard Japan doesn't have any roundabouts as drivers there found them too confusing.
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Re: US and the roundabout

Post by c2R »

Truvelo wrote:I have arrived at a 4 way stop exactly the same time as a car coming from the left or right. I try to avoid this by adjusting my speed but when it happens I just wait for the other vehicle to emerge first. It's better than smashing the hire car and paying a huge excess :)
I really hate the multi-lane four way stops - we came across one in Nevada and it really was tricky to keep track of who should be going and when.
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Re: US and the roundabout

Post by M19 »

Most roundabouts in the US are single lane entry. There has been a lot of research on design for multi-lane roundabouts. They found that whilst more radial entry angles are fine for single lane roundabouts, they cause problems with vehicle path overlap on multi-lane roundabouts.

The presentation via the following link shows nicely why more radial entry angles are unsafe for multi-lane roundabouts. Yet, in the UK, we seem quite happy to be promoting multi-lane roundabouts with dodgy radial entry angles. We have a lot to learn from what the US is learning.

I also like the way that roundabouts are marked in the US. Neater would you agree?

https://www.google.co.uk/url?sa=t&sourc ... Z_XMhj41lV
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Re: US and the roundabout

Post by Bryn666 »

We've completely lost the skill of designing roundabouts in the UK because we start off in the wrong place: what's cheapest.

So a junction that requires a large roundabout gets a diddly one because £££. A classic example is this pile of cack on the A682: https://goo.gl/maps/dyBQdKRE5gK2

Entry path overlap, plus overshooting. Since GSV was there all that Chevroflex has been driven over multiple times. The solution? A 40 mph speed limit on approach, despite the fact this is slap bang in the middle of a former 70 mph sub-motorway specification dual carriageway.

Yes, driver error has a lot to answer for, but for crying out loud at least design something appropriate first.
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Re: US and the roundabout

Post by Burns »

Bryn666 wrote:We've completely lost the skill of designing roundabouts in the UK because we start off in the wrong place: what's cheapest.

So a junction that requires a large roundabout gets a diddly one because £££. A classic example is this pile of cack on the A682: https://goo.gl/maps/dyBQdKRE5gK2
It doesn't even link to anything that isn't served by the next ~roundabout a 1/4 mile away.
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Re: US and the roundabout

Post by bart »

Here's a stealth one. There are no warning signs on approach, the road simply diverges and then each fork is signed individually.

https://goo.gl/maps/cYtmwkNPXu12
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Re: US and the roundabout

Post by Viator »

M19 wrote:I also like the way that roundabouts are marked in the US. Neater would you agree?
Except that that's much too sweeping a statement. The marking and signing of roundabouts in the US is very diverse, being one of those things that is decided state-by-state.
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Re: US and the roundabout

Post by trencheel303 »

Burns wrote:
Bryn666 wrote:We've completely lost the skill of designing roundabouts in the UK because we start off in the wrong place: what's cheapest.

So a junction that requires a large roundabout gets a diddly one because £££. A classic example is this pile of cack on the A682: https://goo.gl/maps/dyBQdKRE5gK2
It doesn't even link to anything that isn't served by the next ~roundabout a 1/4 mile away.
Like most roundabouts smaller than the large multi-lane affairs or off-motorway gyratories, that seems a pointless affair, in my opinion. I hold the (probably unpopular) opinion that roundabouts should be reserved for only large junctions and interchanges that really require it, and not what we see these days which is a fad of small and mini roundabouts which are essentially bast@rdised T junctions.

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Re: US and the roundabout

Post by ScottB5411 »

c2R wrote:
Truvelo wrote:I have arrived at a 4 way stop exactly the same time as a car coming from the left or right. I try to avoid this by adjusting my speed but when it happens I just wait for the other vehicle to emerge first. It's better than smashing the hire car and paying a huge excess :)
I really hate the multi-lane four way stops - we came across one in Nevada and it really was tricky to keep track of who should be going and when.
If 2 cars arrive at the same time or you are unsure the priorité-a-droit rules applies in the states. Unless you're in Louisiana or Mississppi then it's put luck wether you'll have some moron in the side of you who didn't even stop.
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J N Winkler
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Re: US and the roundabout

Post by J N Winkler »

Just to add to the comments upthread:

Rotaries, such as are found in the northeastern states, are not conceptually the same as modern roundabouts in the US, though they have much in common with contemporary British roundabouts. The typical rotary was designed for entering traffic to merge in at speed, so central islands tended to be large while entries had low deflection. This was not considered a safe design, so rotaries in much of the country were reconstructed out of existence while the northeast (in line with eventual British practice following the yield-on-entry experiments in the 1950's and 1960's) retrofitted most of them with yield-on-entry. Example of a former rotary not in the northeast:

I-35/US 62 East in Oklahoma City, Oklahoma (satellite view shows the original roundabout bridges still in use even though their curvature does not match that of the current service-road crossings; interchange roundabout received the hamburger treatment sometime between 1995 and 2002 with construction of a new bridge over I-35; HistoricAerials.com shows the original interchange built sometime between 1954 and 1969)

Single-roundabout freeway interchanges have been tried in the US, but generally dumbbell configurations are preferred. Examples:

I-135/East 1st Street in Newton, Kansas: single-roundabout interchange

Loop 202/East Brown Road in Mesa, Arizona: dumbbell interchange

Roundabout diagrammatics are now in the MUTCD as of the latest (2009) edition, but prior to that there was experimentation with British map-type signs (complete with chamfered stub arms, which are not used anywhere else in the US) and Australian lane-by-lane roundabout diagrammatics. Examples:

Australian-style sign at US 60/US 93 in Wickenburg, Arizona

Map-type sign at Loop 202/McKellips Road in Mesa, Arizona

As for American attitudes to roundabouts, there is a spectrum. Although modern roundabouts have been part of the roadway design and traffic engineering scene in the US for almost 30 years now, some communities are still new to them and there are occasional reports of roundabout phobia. Meanwhile, some local agencies have taken to roundabouts so enthusiastically that they are deployed in marginal use cases. A few examples of the latter:

Malta, New York (six roundabouts visible at the zoom level linked to; a further four nearby)

Watertown, Wisconsin (nine roundabouts part of or near the STH 26 western freeway bypass)

Carmel, Indiana (over a dozen roundabouts visible at various zoom settings, including "squished" ones as part of freeway interchanges along US 31 and the Keystone Parkway; the city hosted a major roundabouts conference several years ago)

A few state DOTs, like New York State DOT and Wisconsin DOT, have policies that favor roundabout construction by requiring signals to be specially justified.
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Re: US and the roundabout

Post by Viator »

J N Winkler wrote:Watertown, Wisconsin (nine roundabouts part of or near the STH 26 western freeway bypass)
Is the attachment of flags (of the fluttering kind) to Yield signs a Wisconsin speciality? Never seen that before! They seem to have been present on most of the signs at this roundabout during a period of at least three years.
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Re: US and the roundabout

Post by Bryn666 »

It's interesting that where the US is now considering roundabouts as the default we are putting in acres of signalised clusterdiddles ostensibly to help pedestrians and cyclists... who then are forced to wait for ages thanks to over complicated staging plans and gain no benefit from lack of facilities beyond a token ASL.

The standards are all to pot in this country and will only get worse as the traffic engineering skills shortage continues. They exist to make life easier for civil engineering design teams, NOT the road users.
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Re: US and the roundabout

Post by Bryn666 »

This is the MUTCD drawing for a multi-lane roundabout. It is so much neater than our mix of dashed lines everywhere. I'd say one of the few examples of American road markings being vastly superior to us.
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Re: US and the roundabout

Post by J N Winkler »

Viator wrote:Is the attachment of flags (of the fluttering kind) to Yield signs a Wisconsin speciality? Never seen that before! They seem to have been present on most of the signs at this roundabout during a period of at least three years.
In this case I think they are a short-term conspicuity treatment. Iowa also uses "flags" to enhance the conspicuity of speed limit signs that indicate a large reduction in the prevailing speed limit, but these are actually squares of metal with retroreflective sheeting on the traffic side and are permanently attached to the signposts.
Bryn666 wrote:It's interesting that where the US is now considering roundabouts as the default we are putting in acres of signalised clusterdiddles ostensibly to help pedestrians and cyclists... who then are forced to wait for ages thanks to over complicated staging plans and gain no benefit from lack of facilities beyond a token ASL.

The standards are all to pot in this country and will only get worse as the traffic engineering skills shortage continues. They exist to make life easier for civil engineering design teams, NOT the road users.
In the US I worry about fiber optic and LEDs giving rise to stoplight cancer. LEDs result in a lower electricity bill to operate signals, while fiber optic is expensive advance provision and thus can push agencies to try to implement network coordination (including the installation of signals at marginal locations) to justify the investment.
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Re: US and the roundabout

Post by M19 »

Bryn666 wrote:This is the MUTCD drawing for a multi-lane roundabout. It is so much neater than our mix of dashed lines everywhere. I'd say one of the few examples of American road markings being vastly superior to us.
Definitely neater and more organised. There's the right amount of deflection and the entry angle is what it should be.
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Re: US and the roundabout

Post by Peter Freeman »

J N Winkler wrote: ... and Australian lane-by-lane roundabout diagrammatics. Examples:

Australian-style sign at US 60/US 93 in Wickenburg, Arizona
I consider the Australian lane-by-lane signs to be very clear and easy to follow. There are many, though they're certainly not universal, even on multi-lane roundabouts. Roundabouts with more than two lanes are uncommon here, and none of them resemble the confusing and frightening giants found in the UK. I especially notice this type of sign when I'm in Adelaide, though I can't quote any numbers.
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Re: US and the roundabout

Post by odlum »

i70.jpg
A dumbell roundabout interchange has appeared on I-70 west of Vail in Colorado
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Re: US and the roundabout

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Another American dumbbell, of fairly recent introduction, on US 33 near Logan OH.
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