Knowing what a roundabout really is

[tolbs17]

Looking at this website, it appears that rotaries are old school (traffic circles) and roundabouts are when you slow down when you approach them.

Aren't traffic calming circles the same thing?

https://roundabouts.kittelson.com/

[Dirt Roads]

Note that the definition of "traffic circle" is dependent on regional preferences.  In some areas, the term "traffic circle" are like the huge ones in England with multiple lanes.  In other areas, they work like 3-way intersections with a stop sign for traffic coming from the third wing.  From what I can tell, there is a third version where "rotaries" using yield signs are differentiated between 3-way intersections (traffic circles) and 4-way (or more) intersections (roundabouts). 

[hbelkins]

Someone's going to jump in and say there are distinct differences between roundabouts, rotaries, traffic circles, and now mini-roundabouts -- primarily over who has the right of way when inside or approaching one -- but I still say they are all the same and I have no use for any of them, not even the quaint ones where the county courthouse is in the middle of one. Although I have to say that those are preferable over the other varieties because the distance between the legs is greater and you have more time to enter the circle when there's oncoming traffic.

[Rothman]

Pfft.  In MA, rotaries operate like roundabouts.

[Rothman]

Someone's going to jump in and say there are distinct differences between roundabouts, rotaries, traffic circles, and now mini-roundabouts -- primarily over who has the right of way when inside or approaching one -- but I still say they are all the same and I have no use for any of them, not even the quaint ones where the county courthouse is in the middle of one. Although I have to say that those are preferable over the other varieties because the distance between the legs is greater and you have more time to enter the circle when there's oncoming traffic.

Saying things are the same when there atr notable differences is willful ignorance.

[CtrlAltDel]

Someone's going to jump in and say there are distinct differences between roundabouts, rotaries, traffic circles, and now mini-roundabouts -- primarily over who has the right of way when inside or approaching one -- but I still say they are all the same and I have no use for any of them, not even the quaint ones where the county courthouse is in the middle of one. Although I have to say that those are preferable over the other varieties because the distance between the legs is greater and you have more time to enter the circle when there's oncoming traffic.

Saying things are the same when there atr notable differences is willful ignorance.

I'm pretty sure that was his intention. He doesn't like them, and so they're beneath his dignity, or something along those lines.

[froggie]

Indeed.  HB has made no secret of his disdain for roundabouts and the like.

[hbelkins]

Indeed.  HB has made no secret of his disdain for roundabouts and the like.

Some choose to die on the Clearview hill. I choose the roundabout hill.

[Road Hog]

It's all splitting hairs, like the difference between a coke, a soft drink, a soda or a pop.

[J N Winkler]

Looking at this website, it appears that rotaries are old school (traffic circles) and roundabouts are when you slow down when you approach them.

Aren't traffic calming circles the same thing?

https://roundabouts.kittelson.com/

Not quite.  A spotter's guide:

*  Rotaries are large-diameter circular intersections.  Many now have the same yield-on-entry rule as modern roundabouts because this has been shown through experimentation to yield better traffic flow, but they were originally designed on the assumption that traffic would enter at speed and the sections between legs would work like weaving lanes.  The old AASHO Blue Book used to have design criteria for rotaries (and examples used to exist outside the Northeast, including in Oklahoma City), but I haven't seen them in any recent edition of the AASHTO Green Book.

*  Traffic calming circles are typically obstacles placed within intersections (typically without revision of the curb returns) to encourage traffic to slow down.  Conceptually, they are similar to chicanes.

*  "Traffic circle" is the highway engineering community's attempt (not quite successful) to differentiate circular intersections that, for various reasons, don't have yield-on-entry (like the one in Paris that has the Arc de Triomphe in the middle).

*  In addition to a yield-on-entry rule, modern roundabouts have deflection on approach and are designed for relatively low circulating speeds (parameters that are manipulated to secure desired operating characteristics include diameter of the circulating carriageway, the degree of deflection, and the amounts of superelevation on approach and crossfall within the roundabout).  They are generally smaller than rotaries.

[Rothman]

It's all splitting hairs, like the difference between a coke, a soft drink, a soda or a pop.

Three of those is splitting hairs.  One of them is evidence of a society allowing a single corporation way too much control over its language.

[Scott5114]

The old AASHO Blue Book used to have design criteria for rotaries (and examples used to exist outside the Northeast, including in Oklahoma City)

Where was this?

It's all splitting hairs, like the difference between a coke, a soft drink, a soda or a pop.

Three of those is splitting hairs.  One of them is evidence of a society allowing a single corporation way too much control over its language.

So you'd never, say, google how much kleenex a dumpster can hold? Or bring some jello up an escalator?

[Tom958]

I believe, perhaps incorrectly, that modern roundabouts are not an evolutionary development. Instead, they were invented in 1956 by British boffins as an entirely new type of intersection, almost coequal with interchanges, that would be of great usefulness during the impending massive expansion of Britain's arterial highway network. While experience with previous circular intersections probably influenced the concept, and while successful elements of the developed concept were then applied to preexisting circular intersections and incorporated into traffic law, that wasn't the main reason why the roundabout was invented.

Why is this important? Because it makes it reasonable to make an effort to learn (and teach!) the principles of roundabout design and usage as general, universal rules, with any exceptions to be regarded as the anomalies they are. Doing this, I believe, would increase the safety and efficiency of roundabouts and bring them closer to living up to their full potential rather than being the most dangerous intersections in some states. However, if a sizable proportion of users of this forum can't understand this, there's very little possibility that the motoring public at large will.

[Rothman]

It's all splitting hairs, like the difference between a coke, a soft drink, a soda or a pop.

Three of those is splitting hairs.  One of them is evidence of a society allowing a single corporation way too much control over its language.

So you'd never, say, google how much kleenex a dumpster can hold? Or bring some jello up an escalator?

No.

[kalvado]

I believe, perhaps incorrectly, that modern roundabouts are not an evolutionary development. Instead, they were invented in 1956 by British boffins as an entirely new type of intersection, almost coequal with interchanges, that would be of great usefulness during the impending massive expansion of Britain's arterial highway network. While experience with previous circular intersections probably influenced the concept, and while successful elements of the developed concept were then applied to preexisting circular intersections and incorporated into traffic law, that wasn't the main reason why the roundabout was invented.

Why is this important? Because it makes it reasonable to make an effort to learn (and teach!) the principles of roundabout design and usage as general, universal rules, with any exceptions to be regarded as the anomalies they are. Doing this, I believe, would increase the safety and efficiency of roundabouts and bring them closer to living up to their full potential rather than being the most dangerous intersections in some states. However, if a sizable proportion of users of this forum can't understand this, there's very little possibility that the motoring public at large will.

You also miss a key part - those who design and build roundabouts have to have that understanding before first shovel of dirt gets moved.

[jeffandnicole]

*  "Traffic circle" is the highway engineering community's attempt (not quite successful) to differentiate circular intersections that, for various reasons, don't have yield-on-entry (like the one in Paris that has the Arc de Triomphe in the middle).

NJ always took the features of a traffic circle a bit further, because there would be gas stations, restaurants and other businesses that would have their primary or only access points within the circle. So along with the non-controlled or yield-within-the-circle features, there would be driveway aprons to access businesses, which often required 90 degree (or sharper) turns to access. The Brooklawn Circle (US 130/NJ 47) features 13 different entry or access points. As several of these are business access points that allow both entry and exit, there's a total of 18 into/out of movements within the circle! And that's *fewer* than before, as at least 1 entry point was removed!

Then to add to that...one circle near me features a gas station...within the center median.
https://maps.app.goo.gl/eJxNqXwt4qmKTgwD8 The main roadways accesses and within the circle are uncontrolled as well

[Tom958]

You also miss a key part - those who design and build roundabouts have to have that understanding before first shovel of dirt gets moved.

Well, yeah. That goes without saying, so I didn't say it.

[formulanone]

Indeed.  HB has made no secret of his disdain for roundabouts and the like.

Some choose to die on the Clearview hill. I choose the roundabout hill.

Well, that's one way to reduce the risk of being hit by a car in the roundabout.

It's all splitting hairs, like the difference between a coke, a soft drink, a soda or a pop.

Three of those is splitting hairs.  One of them is evidence of a society allowing a single corporation way too much control over its language.

So you'd never, say, google how much kleenex a dumpster can hold? Or bring some jello up an escalator?

No.

Sound the klaxon and get the band-aids ready.

[J N Winkler]

The old AASHO Blue Book used to have design criteria for rotaries (and examples used to exist outside the Northeast, including in Oklahoma City)

Where was this?

It was at I-35/US 62 (NE 23rd Street) and was removed when the interchange was rebuilt in (I think) the mid-1980's, though the two overbridges for the circulatory carriageway were retained and used for the crossovers.

I believe, perhaps incorrectly, that modern roundabouts are not an evolutionary development. Instead, they were invented in 1956 by British boffins as an entirely new type of intersection, almost coequal with interchanges, that would be of great usefulness during the impending massive expansion of Britain's arterial highway network. While experience with previous circular intersections probably influenced the concept, and while successful elements of the developed concept were then applied to preexisting circular intersections and incorporated into traffic law, that wasn't the main reason why the roundabout was invented.

This is substantially correct.  The focus of the British research in the late 1950's and through the 1960's was indeed on improving capacity and traffic operation for roundabouts, first by imposing a yield-on-entry rule and then through other measures to prevent lock-up, such as adding mini-roundabouts within the circulatory carriageway of a larger roundabout (resulting in "magic roundabouts," the technical term for which was "ring junctions").  And it is true that a "big bang" in highway infrastructure provision occurred beginning in the late 1950's.  However, most of the roundabouts built as part of motorway junctions and so on were roughly the size of AASHO rotaries.

What is now called the "modern" roundabout, with small inscribed circle diameter, was developed later in Australia, France, Germany, and the US.  Some British engineers have actually adopted elements of the basic design approach (such as outward drainage in the circulatory carriageway) from the US for newer roundabouts built as part of housing estates and the like.

NJ always took the features of a traffic circle a bit further, because there would be gas stations, restaurants and other businesses that would have their primary or only access points within the circle. So along with the non-controlled or yield-within-the-circle features, there would be driveway aprons to access businesses, which often required 90 degree (or sharper) turns to access. The Brooklawn Circle (US 130/NJ 47) features 13 different entry or access points. As several of these are business access points that allow both entry and exit, there's a total of 18 into/out of movements within the circle! And that's *fewer* than before, as at least 1 entry point was removed!

Then to add to that...one circle near me features a gas station...within the center median.
https://maps.app.goo.gl/eJxNqXwt4qmKTgwD8 The main roadways accesses and within the circle are uncontrolled as well

This reminds me of gas stations within the footprint of loop ramps, another unusual and regionally specific feature from the 1960's.

[empirestate]

Looking at this website, it appears that rotaries are old school (traffic circles) and roundabouts are when you slow down when you approach them.

Aren't traffic calming circles the same thing?

https://roundabouts.kittelson.com/

The important thing to remember is that the various terms are, to a large extent, merely regional or dialectal differences. That they tend to share any common design elements is essentially coincidental.

This particular site uses its own specific jargon to define the different types of junctions, but those aren't necessarily representative of common usage.

[hbelkins]

So does anyone want to delve into the difference between a roundabout and a mini-roundabout?

[froggie]

So does anyone want to delve into the difference between a roundabout and a mini-roundabout?

MnDOT (well, FHWA) already has...

[Tom958]

I believe, perhaps incorrectly, that modern roundabouts are not an evolutionary development. Instead, they were invented in 1956 by British boffins as an entirely new type of intersection, almost coequal with interchanges, that would be of great usefulness during the impending massive expansion of Britain's arterial highway network. While experience with previous circular intersections probably influenced the concept, and while successful elements of the developed concept were then applied to preexisting circular intersections and incorporated into traffic law, that wasn't the main reason why the roundabout was invented.

This is substantially correct.  The focus of the British research in the late 1950's and through the 1960's was indeed on improving capacity and traffic operation for roundabouts, first by imposing a yield-on-entry rule and then through other measures to prevent lock-up, such as adding mini-roundabouts within the circulatory carriageway of a larger roundabout (resulting in "magic roundabouts," the technical term for which was "ring junctions").  And it is true that a "big bang" in highway infrastructure provision occurred beginning in the late 1950's.  However, most of the roundabouts built as part of motorway junctions and so on were roughly the size of AASHO rotaries.

Yes, I rather glossed over that. 

One thing that annoys me about the discourse over modern roundabouts in the US is the fact that it's a great deal easier for drivers to see and comprehend the path they need to take through a compact modern roundabout that it is to do the same through one of these gigantic British circles. Yet the British persisted, apparently largely successfully, while many modern American users and critics give up on the easier ones without even really trying. WTF?

What is now called the "modern" roundabout, with small inscribed circle diameter, was developed later in Australia, France, Germany, and the US.  Some British engineers have actually adopted elements of the basic design approach (such as outward drainage in the circulatory carriageway) from the US for newer roundabouts built as part of housing estates and the like.

So, I suppose there was a second round of boffinery. I wonder if there was much international collaboration in the days before the Internet, or if the teams in various nations arrived at similar conclusions independently. Probably a bit of both.

[kalvado]

I believe, perhaps incorrectly, that modern roundabouts are not an evolutionary development. Instead, they were invented in 1956 by British boffins as an entirely new type of intersection, almost coequal with interchanges, that would be of great usefulness during the impending massive expansion of Britain's arterial highway network. While experience with previous circular intersections probably influenced the concept, and while successful elements of the developed concept were then applied to preexisting circular intersections and incorporated into traffic law, that wasn't the main reason why the roundabout was invented.

This is substantially correct.  The focus of the British research in the late 1950's and through the 1960's was indeed on improving capacity and traffic operation for roundabouts, first by imposing a yield-on-entry rule and then through other measures to prevent lock-up, such as adding mini-roundabouts within the circulatory carriageway of a larger roundabout (resulting in "magic roundabouts," the technical term for which was "ring junctions").  And it is true that a "big bang" in highway infrastructure provision occurred beginning in the late 1950's.  However, most of the roundabouts built as part of motorway junctions and so on were roughly the size of AASHO rotaries.

Yes, I rather glossed over that. 

One thing that annoys me about the discourse over modern roundabouts in the US is the fact that it's a great deal easier for drivers to see and comprehend the path they need to take through a compact modern roundabout that it is to do the same through one of these gigantic British circles. Yet the British persisted, apparently largely successfully, while many modern American users and critics give up on the easier ones without even really trying. WTF?

What is now called the "modern" roundabout, with small inscribed circle diameter, was developed later in Australia, France, Germany, and the US.  Some British engineers have actually adopted elements of the basic design approach (such as outward drainage in the circulatory carriageway) from the US for newer roundabouts built as part of housing estates and the like.

So, I suppose there was a second round of boffinery. I wonder if there was much international collaboration in the days before the Internet, or if the teams in various nations arrived at similar conclusions independently. Probably a bit of both.

Hard to beat a good old intersection in terms of easy navigation, though.

[froggie]

^ Depends on your definition of "easy".  Sitting at a red signal for a minute or two isn't "easy" for many people.  And it's well documented that, all else being equal, a roundabout results in less overall delay than a "good ol' intersection".