Modern roundabouts in America

[tradephoric]

Download the .KMZ to view in Google Earth!
last update Dec. 2013 - http://www.mediafire.com/download/qo07f0wdr8kl72d/Modern%20roundabouts%20(USA).kmz

Modern roundabouts in the lower 48:


The KMZ file includes roughly 3,200 known modern roundabouts throughout the United States.  The modern roundabouts are split up into 3 main categories: local roundabouts, major roundabouts, and interchange roundabouts.  In addition, the modern roundabouts are split up based on the number of circulating lanes: single-lane, multi-lane, and triple-lane.  The historic imagery feature in GE was used to determine the approximate year of construction.  Since there can be large gaps between imagery dates, the year of construction is approximate only.

Not sure how this thread will progress, but any comments or suggestions are welcomed!

[hotdogPi]

I do not see NY 206 / CR 39. (It's right next to I-88.)

EDIT: It doesn't seem to be working when I download it.

[tradephoric]

^^^ I created another version without time slider data.  Time slider files in GE can be difficult to navigate at times.  Try this version and see if it helps:

http://www.mediafire.com/download/5kasnb3v4apq70b/Modern+roundabouts+%28USA%29+no+timeslide.kmz

[hotdogPi]

I just don't know where to put the file.

[Zeffy]

Open it in Google Earth. So save it to somewhere (Desktop, Downloads folder, etc.) and launch Google Earth and go to File->Open then go to wherever you saved the file.

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

[hotdogPi]

I can't open Google Earth. I can use it by clicking the icon on Google Maps, but I can't open Google Earth by itself.

The download is currently in my desktop.

It won't let me open the file with Google Earth either.


I use Mac, so it might not work.

[Zeffy]

Well, looking at Google's site, it is compatible with Mac OSes... I'm not sure why it won't open in standalone - administrative privileges maybe?

[NE2]

What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

The same as the difference between light rail and streetcar: marketing.
And maybe a somewhat better design in some cases.
http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa08006/

PS: if it goes in and around a lake it's a roundabout.

[hotdogPi]

I was opening the wrong thing.

But now, whenever I try to open it, it tries to install it instead.

It has already been installed twice.

I have:

Modern roundabouts (USA) no timeslide.kmz (Google Earth KMZ Document)
googleearth-mac-plugin-intel.dmg.download (Safari download)
googleearth-mac-plugin-intel.dmg (Disk image)
Google Earth Web Plug-in.plugin (Plug-in)
Google Earth (Volume)

[countysigns]

A couple new modern roundabouts opened up recently at the exit ramps from US-23 to US-223 in Monroe County, MI...one on each side of the interchange.

[DaBigE]

Open it in Google Earth. So save it to somewhere (Desktop, Downloads folder, etc.) and launch Google Earth and go to File->Open then go to wherever you saved the file.

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

In a word, size. Traffic circles are generally much smaller, typically found on low-volume (neighborhood) streets, and usually lack splitter islands on the approaches. They are more for traffic calming (read: an attempt in passive speed control) rather than an intersection capacity tool.

Rotaries, OTOH, are usually much larger than the modern roundabout. Some places have replaced rotaries with roundabouts and the roundabout fit inside the grassy center of the old rotary. Rotaries operate differently as well, with circulating traffic yielding to entering traffic. Speeds are generally much higher, and in some cases, parking is allowed around the circle as well.

[Kacie Jane]

Open it in Google Earth. So save it to somewhere (Desktop, Downloads folder, etc.) and launch Google Earth and go to File->Open then go to wherever you saved the file.

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

In a word, size. Traffic circles are generally much smaller, typically found on low-volume (neighborhood) streets, and usually lack splitter islands on the approaches. They are more for traffic calming (read: an attempt in passive speed control) rather than an intersection capacity tool.

Rotaries, OTOH, are usually much larger than the modern roundabout. Some places have replaced rotaries with roundabouts and the roundabout fit inside the grassy center of the old rotary. Rotaries operate differently as well, with circulating traffic yielding to entering traffic. Speeds are generally much higher, and in some cases, parking is allowed around the circle as well.

What you're calling a rotary is what Zeffy is calling a traffic circle.  Here's Flemington Circle (as well as a second circle just to the west) on Google Maps. https://goo.gl/maps/PrKY3

[DaBigE]

Open it in Google Earth. So save it to somewhere (Desktop, Downloads folder, etc.) and launch Google Earth and go to File->Open then go to wherever you saved the file.

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

In a word, size. Traffic circles are generally much smaller, typically found on low-volume (neighborhood) streets, and usually lack splitter islands on the approaches. They are more for traffic calming (read: an attempt in passive speed control) rather than an intersection capacity tool.

Rotaries, OTOH, are usually much larger than the modern roundabout. Some places have replaced rotaries with roundabouts and the roundabout fit inside the grassy center of the old rotary. Rotaries operate differently as well, with circulating traffic yielding to entering traffic. Speeds are generally much higher, and in some cases, parking is allowed around the circle as well.

What you're calling a rotary is what Zeffy is calling a traffic circle.  Here's Flemington Circle (as well as a second circle just to the west) on Google Maps. https://goo.gl/maps/PrKY3

Now after seeing Flemington Circle, I'm not really sure what it would be called, at least based on the current satellite image. It's sized like a rotary, and on some approaches, operates like a rotary (NB & WB, yields to entering traffic), but operates like a modern roundabout (entering traffic yields to circulating).

The one on to the west is sized like a rotary, but operates like a modern roundabout (all yield to circulating).

FWIW, local terminology does not always match engineering terminology. That is one of the biggest hurdles to overcome when presenting a new roundabout project. The first argument I usually hear at a public meeting is how the east coast has "tons of roundabouts that they're ripping out". In actuality, it's rotaries that are being replaced, not modern roundabouts. Wikipedia has a fairly good write-up separating the three intersection types.

Roundabout
Traffic Circle
Roundabout
Traffic Circle

[tradephoric]

The circle directly to the west of Flemington Circle is interesting.  Looking at the historical imagery from 2009, it's apparent that it operated as a traffic circle with circulating traffic yielding to entering traffic.  The circle was recently upgraded so that it now has nearly all the design characteristics of a modern roundabout (all entering traffic yields, raised splitter islands, sharper entry angles to slow entering vehicles, an added truck apron, and upgraded pavement markings).  Here is a current aerial of the circle:



Although it may look like a modern roundabout, it doesn't function as one due to its sheer size (that's one thing that didn't change with the upgrade).  The diameter of the central island plus the width of the truck apron is approaching 300 feet.  Such a large diameter allows for higher circulating speeds which can create a big speed differential between entering and circulating traffic.  The whole idea of a modern roundabout is to keep speeds down.  Just looking at that aerial, you could drive through the circle at 60 M.P.H. if you really wanted to.  I wouldn't consider this a modern roundabout.

[roadfro]

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

In a word, size. Traffic circles are generally much smaller, typically found on low-volume (neighborhood) streets, and usually lack splitter islands on the approaches. They are more for traffic calming (read: an attempt in passive speed control) rather than an intersection capacity tool.

Rotaries, OTOH, are usually much larger than the modern roundabout. Some places have replaced rotaries with roundabouts and the roundabout fit inside the grassy center of the old rotary. Rotaries operate differently as well, with circulating traffic yielding to entering traffic. Speeds are generally much higher, and in some cases, parking is allowed around the circle as well.

What you're calling a rotary is what Zeffy is calling a traffic circle.  Here's Flemington Circle (as well as a second circle just to the west) on Google Maps. https://goo.gl/maps/PrKY3

Now after seeing Flemington Circle, I'm not really sure what it would be called, at least based on the current satellite image. It's sized like a rotary, and on some approaches, operates like a rotary (NB & WB, yields to entering traffic), but operates like a modern roundabout (entering traffic yields to circulating).

The one on to the west is sized like a rotary, but operates like a modern roundabout (all yield to circulating).

FWIW, local terminology does not always match engineering terminology. That is one of the biggest hurdles to overcome when presenting a new roundabout project. The first argument I usually hear at a public meeting is how the east coast has "tons of roundabouts that they're ripping out". In actuality, it's rotaries that are being replaced, not modern roundabouts. Wikipedia has a fairly good write-up separating the three intersection types.

Roundabout
Traffic Circle
Roundabout
Traffic Circle

It can be explained that traffic circles are one classification of road junction with various subsets that include rotaries and roundabouts–similar to how interchanges are another type of junction, which includes as subsets diamond interchanges, cloverleafs, parclos, SPUIs, DDIs, directional stacks, etc.

In the U.S., however, the terms "traffic circle" and "rotary" are often used interchangeably. In traffic engineering terminology, these are distinguished from "modern roundabouts" by design characteristics which include size, certain design features, and operational patterns.

Rotaries are the bigger circles that tend to have higher speeds. They are not necessarily yield on entry. In some cases they may have no official traffic controls; sometimes the entry or circulating traffic may be controlled by stop signs or traffic signals (like various circles in Washington DC for example). The central island may sometimes feature a small park or other place for pedestrians. These are the junctions that were typical in areas like New Jersey that in some cases are being ripped out or redesigned. The Flemington Circle mentioned previously is a traffic circle or rotary–notice the large size and the couple branches where the circulating traffic is to yield to the entering traffic on some of the heavy movements.

Roundabouts are smaller circles which have lower speeds. Entering traffic always yields to traffic already in the circular roadway. No pedestrians are permitted on the central island. Correctly-designed modern roundabouts at larger junctions will have appropriate channelization so as to funnel circulating traffic to particular exits (preventing continuous circulation, if following the markings).

What DaBigE is calling "traffic circles" above are actually more correctly referred to as "mini roundabouts". These are intersections typically in residential areas with a small island in the center that operate as roundabout, but the surroundings don't permit (and traffic volumes don't require) full roundabout build-out. Splitter islands and channelization are usually absent from mini roundabouts. Mini roundabouts are most often implemented as a neighborhood traffic calming measure.

[NE2]

What DaBigE is calling "traffic circles" above are actually more correctly referred to as "mini roundabouts". These are intersections typically in residential areas with a small island in the center that operate as roundabout, but the surroundings don't permit (and traffic volumes don't require) full roundabout build-out. Splitter islands and channelization are usually absent from mini roundabouts. Mini roundabouts are most often implemented as a neighborhood traffic calming measure.

Supposedly a mini roundabout has only paint so larger vehicles can go straight through. If there's a solid island it's not a mini roundabout no matter how small it is. Or so say the more anal OSM mappers: http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout#Possible_misinterpretations

[froggie]

Another consideration to factor:  roundabouts ALWAYS give traffic within the circle the right-of-way.  That's often not the case with traffic circles.  Also concur with roadfro's last paragraph..."mini-roundabout" is the generally accepted engineering and planning parlance for what DaBigE called a "traffic circle".

Here's a comparison list posted by VDOT with info originating from WisDOT about the differences between roundabouts and traffic circles.

The traffic circles Zeffy referred to upthread would not be in the KMZ file because they are not roundabouts nor do they function like roundabouts.  Especially in the case of Flemington Circle where traffic in the circle yields to traffic entering on US 202.

Meanwhile...

I use Mac, so it might not work.

Worked just fine on my Mac.

For tradephoric:  out of curiosity, I looked up one roundabout in particular, in Amherst, VA.  I understand you're going by the limits of available imagery in Google Earth, but the US 60/BUSINESS US 29 roundabout was built and has been operating as such since 1936.  It was upgraded in 2004.  You're also missing the long-standing US 15/US 33/VA 231 roundabout in Gordonsville, VA, but I haven't been able to pin down the date of its construction yet.

There's also a brand new roundabout at BUSINESS US 13/VA 126/VA 316 on the Virginia Eastern Shore, just completed last month.

[Zeffy]

After reading the various responses to my question, I understand that there is a difference between those and roundabouts / rotaries. So, here's some Google Maps views of some other circles in New Jersey that I want your opinion on:





Out of all of these, I only think that the US 130 circle (last picture) is a roundabout - the others I can't tell whether they would be classified as a rotary or a traffic circle.

[NE2]

Rotaries are traffic circles. Any difference is made up.

That last one at US 130 and NJ 47 is not a roundabout - note that entering traffic has right-of-way in two places.

[tradephoric]

For tradephoric:  out of curiosity, I looked up one roundabout in particular, in Amherst, VA.  I understand you're going by the limits of available imagery in Google Earth, but the US 60/BUSINESS US 29 roundabout was built and has been operating as such since 1936.  It was upgraded in 2004.  You're also missing the long-standing US 15/US 33/VA 231 roundabout in Gordonsville, VA, but I haven't been able to pin down the date of its construction yet.

I can update the construction year for the Amherst, VA roundabout as 2004 for the next release.  Looking at the aerial from 1994, it looked like the circle had the characteristics of a modern roundabout but the aerial was really too grainy to make it out.  For some roundabouts, the earliest aerial imagery available was from 2002 and the modern roundabout was already constructed.  Since it's generally accepted that the first modern roundabout was constructed in 1990, that leaves a big gap of potential years when the roundabout could have been constructed.  I probably wouldn't put that much stock in the construction year.  I'd guess 90% are accurate within +/- a year while the other 10% might be a ways off.

I didn't include the Gordonsville, VA circle because i don't believe it's a modern roundabout.  One of the entering approaches has stop sign control and you can literally drive through the circle in a straight line.

There's also a brand new roundabout at BUSINESS US 13/VA 126/VA 316 on the Virginia Eastern Shore, just completed last month.

There's a folder called "unknown" that is originally unticked when you open the KMZ file.  This folder includes modern roundabouts that are either planned or have been constructed but Google hasn't updated the aerial imagery in the area yet.  The roundabout you mention is included in the unknown folder.

[DaBigE]

Nice work though, though I have one question that might be slightly off-topic. What is the difference between a roundabout and a traffic circle? I say this because I expected the Somerville Circle, the Flemington Circle, the Airport Circle, etc. to be in the collection, but they're not, which I guess means they are different than roundabouts. At a precursory glance, there doesn't seem to be a difference, but I feel like it's something small.

In a word, size. Traffic circles are generally much smaller, typically found on low-volume (neighborhood) streets, and usually lack splitter islands on the approaches. They are more for traffic calming (read: an attempt in passive speed control) rather than an intersection capacity tool.

Rotaries, OTOH, are usually much larger than the modern roundabout. Some places have replaced rotaries with roundabouts and the roundabout fit inside the grassy center of the old rotary. Rotaries operate differently as well, with circulating traffic yielding to entering traffic. Speeds are generally much higher, and in some cases, parking is allowed around the circle as well.

What you're calling a rotary is what Zeffy is calling a traffic circle.  Here's Flemington Circle (as well as a second circle just to the west) on Google Maps. https://goo.gl/maps/PrKY3

Now after seeing Flemington Circle, I'm not really sure what it would be called, at least based on the current satellite image. It's sized like a rotary, and on some approaches, operates like a rotary (NB & WB, yields to entering traffic), but operates like a modern roundabout (entering traffic yields to circulating).

The one on to the west is sized like a rotary, but operates like a modern roundabout (all yield to circulating).

FWIW, local terminology does not always match engineering terminology. That is one of the biggest hurdles to overcome when presenting a new roundabout project. The first argument I usually hear at a public meeting is how the east coast has "tons of roundabouts that they're ripping out". In actuality, it's rotaries that are being replaced, not modern roundabouts. Wikipedia has a fairly good write-up separating the three intersection types.

Roundabout
Traffic Circle
Roundabout
Traffic Circle

It can be explained that traffic circles are one classification of road junction with various subsets that include rotaries and roundabouts—similar to how interchanges are another type of junction, which includes as subsets diamond interchanges, cloverleafs, parclos, SPUIs, DDIs, directional stacks, etc.

In the U.S., however, the terms "traffic circle" and "rotary" are often used interchangeably. In traffic engineering terminology, these are distinguished from "modern roundabouts" by design characteristics which include size, certain design features, and operational patterns.

Rotaries are the bigger circles that tend to have higher speeds. They are not necessarily yield on entry. In some cases they may have no official traffic controls; sometimes the entry or circulating traffic may be controlled by stop signs or traffic signals (like various circles in Washington DC for example). The central island may sometimes feature a small park or other place for pedestrians. These are the junctions that were typical in areas like New Jersey that in some cases are being ripped out or redesigned. The Flemington Circle mentioned previously is a traffic circle or rotary—notice the large size and the couple branches where the circulating traffic is to yield to the entering traffic on some of the heavy movements.

Roundabouts are smaller circles which have lower speeds. Entering traffic always yields to traffic already in the circular roadway. No pedestrians are permitted on the central island. Correctly-designed modern roundabouts at larger junctions will have appropriate channelization so as to funnel circulating traffic to particular exits (preventing continuous circulation, if following the markings).

What DaBigE is calling "traffic circles" above are actually more correctly referred to as "mini roundabouts". These are intersections typically in residential areas with a small island in the center that operate as roundabout, but the surroundings don't permit (and traffic volumes don't require) full roundabout build-out. Splitter islands and channelization are usually absent from mini roundabouts. Mini roundabouts are most often implemented as a neighborhood traffic calming measure.

Not always. In the case of the second traffic circle example I posted, two approaches have a STOP sign. According to FHWA's Mini-Roundabout definition:

Mini-roundabouts are distinguished from neighborhood traffic circles primarily by their traversable islands and yield control on all approaches, which allows them to function as other roundabouts do. Neighborhood traffic circles are typically built at the intersections of local streets for reasons of traffic calming and/or aesthetics. They typically are operated as two-way or all-way stop-controlled intersections and frequently do not include raised channelization to guide approaching traffic into the circulatory roadway. At some neighborhood traffic circles, left-turning vehicles must turn in front of the central island, potentially conflicting with other circulating traffic.

To help promote safe operations, the design of mini-roundabouts generally aligns passenger cars on the approach in such a way as to naturally follow the circulatory roadway and minimize running over the central island to the extent possible. Due to the small footprint, large vehicles are typically required to over-run the fully traversable central island

All of what has been mentioned so far fall under the category of circular intersections. Traffic circles are more of a gray area, especially with what region of the country you are dealing with. Older traffic circles can be the size of some rotaries and can contain similar features, but usually operate at the speeds of a modern roundabout. Newer traffic circles usually are much smaller, similar to mini-roundabouts.

[Zeffy]

Rotaries are traffic circles. Any difference is made up.

If rotaries are traffic circles, then are traffic circles rotaries? 

No but seriously, I think I'll continue to call them circles, seeing as how that's how New Jersey refers to them:

[tradephoric]

For what it's worth, these are the terms I've heard used to describe the small diameter circles found on low-volume streets:

Traffic calming circle (circular island non-transversable)
Neighborhood traffic circle (circular island non-transversable)
Mini-roundabout (circular island transversable)

The KMZ file doesn't include any of these small diameter circles.  If the diameter of the central island plus the width of the truck apron was less than 50 feet, it wasn't included. 

[roadfro]

What DaBigE is calling "traffic circles" above are actually more correctly referred to as "mini roundabouts". These are intersections typically in residential areas with a small island in the center that operate as roundabout, but the surroundings don't permit (and traffic volumes don't require) full roundabout build-out. Splitter islands and channelization are usually absent from mini roundabouts. Mini roundabouts are most often implemented as a neighborhood traffic calming measure.

Not always. In the case of the second traffic circle example I posted, two approaches have a STOP sign. According to FHWA's Mini-Roundabout definition:

Mini-roundabouts are distinguished from neighborhood traffic circles primarily by their traversable islands and yield control on all approaches, which allows them to function as other roundabouts do. Neighborhood traffic circles are typically built at the intersections of local streets for reasons of traffic calming and/or aesthetics. They typically are operated as two-way or all-way stop-controlled intersections and frequently do not include raised channelization to guide approaching traffic into the circulatory roadway. At some neighborhood traffic circles, left-turning vehicles must turn in front of the central island, potentially conflicting with other circulating traffic.

To help promote safe operations, the design of mini-roundabouts generally aligns passenger cars on the approach in such a way as to naturally follow the circulatory roadway and minimize running over the central island to the extent possible. Due to the small footprint, large vehicles are typically required to over-run the fully traversable central island

All of what has been mentioned so far fall under the category of circular intersections. Traffic circles are more of a gray area, especially with what region of the country you are dealing with. Older traffic circles can be the size of some rotaries and can contain similar features, but usually operate at the speeds of a modern roundabout. Newer traffic circles usually are much smaller, similar to mini-roundabouts.

Well... I didn't know there was a difference between mini roundabouts and neighborhood traffic circles. Any small circle I've ever seen on residential streets has functioned as a mini roundabout--all are yield on entry and didn't have a traversable island.

[empirestate]

rotary : traffic circle :: pop : soda

roundabout : traffic circle :: diet cola : soda