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Rotaries, Roundabouts, and Traffic Circles

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I recently read that parts of Canada are converting some intersections to the rotary format, and some US states are considering building more as well. The reasons are

Safety - traffic all moves and yields in one direction and naturally has to slow down

Gasoline savings - traffic keeps moving instead of having to sit at a full stop

Traffic flow - not having a stop/start pattern keeps cars moving so fewer traffic jams at intersections.

Disadvantages are that they are harder for pedestrians to navigate, and when traffic is very heavy you sometimes still need traffic signals to regulate cars entering the circle.

The problem is that Americans tend to hate them. In some US cities there has been very vocal opposition to building more. Can they ever catch on here? As far as I know, the only one in Houston is at Washington and Westcott.

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I recently read that parts of Canada are converting some intersections to the rotary format, and some US states are considering building more as well. The reasons are

Safety - traffic all moves and yields in one direction and naturally has to slow down

Gasoline savings - traffic keeps moving instead of having to sit at a full stop

Traffic flow - not having a stop/start pattern keeps cars moving so fewer traffic jams at intersections.

Disadvantages are that they are harder for pedestrians to navigate, and when traffic is very heavy you sometimes still need traffic signals to regulate cars entering the circle.

The problem is that Americans tend to hate them. In some US cities there has been very vocal opposition to building more. Can they ever catch on here? As far as I know, the only one in Houston is at Washington and Westcott.

Montrose & Main, and there is one under the Gulf Freeway at Park Place & Broadway.

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The only one I've had experience with is in Pinehurst, NC. There are maybe 25k people in the area during the summer and the rotarty could get pretty congested from time to time. Do you know what parts of Canada are adopting the rotaries?

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I strongly oppose the use of unregulated traffic circles for arterial streets, as congestion in one direction can obstruct traffic going in the other three directions. The most problematic thoroughfares, such as SH6, need overpasses. However, traffic circles in residential neighbourhoods would be greatly beneficial, as an alternative to frequent stop signs.

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Montrose & Main, and there is one under the Gulf Freeway at Park Place & Broadway.

I really wouldn't call the broadway, freeway, park place, a true traffic circle in the sense that it's controlled by a light and it's STILL a pain to navigate.

If the circle was larger in diameter then it would be more successful in managing traffic, as it current stands, it's a hazard on how it's designed.

I strongly oppose the use of unregulated traffic circles for arterial streets, as congestion in one direction can obstruct traffic going in the other three directions. The most problematic thoroughfares, such as SH6, need overpasses. However, traffic circles in residential neighbourhoods would be greatly beneficial, as an alternative to frequent stop signs.

I wish I can find the picture, but I spotted a traffic circle that showed this very problem. The picture doesn't show the ENTIRE story as to why the traffic was stopped or how long, but the results were quite obvious.

The problem I see with the Montrose/Main circle is merging from Herman Park Drive and Montrose can be quite iffy, especially if you have a timid driver or two clogging the works. The best plan I've seen is to simply not stop but accelerate and merge as quickly as you can. It gives as much of a speed racer adrenaline rush as the Allen parkway/45N onramp, but safer.

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I wish I can find the picture, but I spotted a traffic circle that showed this very problem. The picture doesn't show the ENTIRE story as to why the traffic was stopped or how long, but the results were quite obvious.

The problem I see with the Montrose/Main circle is merging from Herman Park Drive and Montrose can be quite iffy, especially if you have a timid driver or two clogging the works. The best plan I've seen is to simply not stop but accelerate and merge as quickly as you can. It gives as much of a speed racer adrenaline rush as the Allen parkway/45N onramp, but safer.

I don't know which picture you speak of, but this will do:

china_468x312.jpg

Notice that all four inbound directions are stuck, where as all four outbound roadways are almost empty.

Traffic circles are notorious for becoming completely gridlocked: cars become unable to move in any direction once different streams of traffic get in each others' ways. The above picture could easily be Westheimer/SH6 or Bellaire/BW8. No thanks - organised grief is superior to chaotic grief.

Edited by desirous

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I don't know which picture you speak of, but this will do:

china_468x312.jpg

Notice that all four inbound directions are stuck, where as all four outbound roadways are almost empty.

Traffic circles are notorious for becoming completely gridlocked: cars become unable to move in any direction once different streams of traffic get in each others' ways. The above picture could easily be Westheimer/SH6 or Bellaire/BW8. No thanks - organised grief is superior to chaotic grief.

That's exactly the picture I was referring to.

But it doesn't tell exactly WHY it's the way it is. Was there an accident that happened just off the circle that made this the aftermath?

How much movement was there and is this common place? Are police dispatched occasionally to resolve this?

Circles are good, but it's the overall design that depends on the success of it.

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The roundabout on Kelly crossing US59 was a death trap! I hated that damned thing. The one at Gulf Freeway was bad until they put the lights in. There was and may still be one on the south end of Washburn Tunnel. I didn't mind that one for some reason. Seems like it was much larger than the others.

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the circle at mecom fountain (main/montrose) can get a little scary during peak times heading north on main because of the overflow of cars waiting to turn left onto montrose. eventually two of the three lanes end up at a standstill, which is bad for the folks that come screaming around the corner.

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<raises hand>

I'm screaming around the corner, but I usually know of that trap and act accordingly.

Still, it makes that part of main exciting!

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Do you know what parts of Canada are adopting the rotaries?

I think it was Ontario.

After having lived in the land of the roundabouts for a few months, my opinion is mixed. For the most part, they seem to do a good job regulating traffic flow, one photograph notwithstanding, and major backups seem rare but not unheard of. I love being able to drive hundreds of miles without hitting a single traffic light. That said, circles at many urban intersections still need lights to regulate traffic. It can be confusing in the larger circles trying to figure out which lane you need to be in. I think they have to be consistent and well-designed to work.

At the Mecom fountain circle, does Main St traffic have to yield on entering the circle, or is it just Montrose and Hermann Park traffic?

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That's exactly the picture I was referring to.

But it doesn't tell exactly WHY it's the way it is. Was there an accident that happened just off the circle that made this the aftermath?

How much movement was there and is this common place? Are police dispatched occasionally to resolve this?

Circles are good, but it's the overall design that depends on the success of it.

There doesn't need to be an accident to produce this type of automotive logjam. Look carefully, and you would see that each direction's traffic flow is blocking another one. Kinda reminiscent of the Oppenheimer Funds logo. Look at the column of cars heading towards the top right of the picture. There is no way it can pass the solid wall of buses in front of it. This is basically the functional equivalent of a full dead-end, and when it gets bad, you have all four directions facing a dead end at the traffic circle intersection.

The greatest weakness of traffic circles is that through traffic has to negotiate with a hefty volume of crossing through traffic just to keep going straight. Four massive columns of solid through traffic are rarely able to smoothly progress past one another - it defies the physics of cars and the biology of human reactions. As mentioned above, the way around this is to augment high-capacity arterial intersections (such as this one in Xiamen, China) with grade-separated through lanes. That would be like Houston highway intersections (e.g., 1960/249) but with a traffic circle replacing the frontage road box. Driver courtesy (something altogether missing in China, I hear) would help as well - don't get in the way of other people if it doesn't get you anywhere.

Edited by desirous

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When I see those all I can think of is :

Clark Griswold: [Reapedly saying it while he can't turn left] Hey look kids, there's Big Ben, and there's Parliament.

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The problem I see with the Montrose/Main circle is merging from Herman Park Drive and Montrose can be quite iffy, especially if you have a timid driver or two clogging the works. The best plan I've seen is to simply not stop but accelerate and merge as quickly as you can. It gives as much of a speed racer adrenaline rush as the Allen parkway/45N onramp, but safer.

IMO it is the driver who is too cautious that causes the majority of the problems. and with no lights, sometimes you end up waiting too long because some drivers want to make sure the circle is clear before proceeding.

Edited by musicman

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Funny, I thought I said some of that.

One of the bad things about the that circle is that you have no clear view, but they may also be it' bonus because it would give you the illusion of people driving towards you!

It's one thing to be a timid driver, but there is something to be said about being slightly aggressive when you're driving which what the circles require, along with a slight amount of courtesy and common sense, of course.

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<<I really wouldn't call the broadway, freeway, park place, a true traffic circle in the sense that it's controlled by a light and it's STILL a pain to navigate.

If the circle was larger in diameter then it would be more successful in managing traffic, as it current stands, it's a hazard on how it's designed. >>

Well, hate to disgree with you there - but when it was first constructed, there were NO LIGHTS! I know, I lived there. That's why they called it "suicide circle". It was meant to flow on its own, first only with yield signs, then stop signs, then, eventually, traffic lights.

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Well, hate to disgree with you there - but when it was first constructed, there were NO LIGHTS! I know, I lived there. That's why they called it "suicide circle". It was meant to flow on its own, first only with yield signs, then stop signs, then, eventually, traffic lights.

i'm not sure if the lights helped the situation there either. the portion on the eastside of the freeway is still horrible.

Edited by musicman

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<<I really wouldn't call the broadway, freeway, park place, a true traffic circle in the sense that it's controlled by a light and it's STILL a pain to navigate.

If the circle was larger in diameter then it would be more successful in managing traffic, as it current stands, it's a hazard on how it's designed. >>

Well, hate to disgree with you there - but when it was first constructed, there were NO LIGHTS! I know, I lived there. That's why they called it "suicide circle". It was meant to flow on its own, first only with yield signs, then stop signs, then, eventually, traffic lights.

By the way, does anyone have either a picture of "suicide circle" the way it was, or an arial picture of the way it is now.

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Hasn't everyone experienced similar logjams on Houston's streets before? Like at a blinking traffic signal on one of our busier thoroughfares?

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Hasn't everyone experienced similar logjams on Houston's streets before? Like at a blinking traffic signal on one of our busier thoroughfares?

That's a technical malfunction. Nothing has to break for the above image to materialise.

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But traffic signals and traffic lights are supposed to give congested lanes greater priority, and it looks like that is what is happening in that picture. The difference between signals and circles is that one is supposed to do it by timer and one is supposed to do it automatically.

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By the way, does anyone have either a picture of "suicide circle" the way it was, or an arial picture of the way it is now.

there is a picture of the circle when I-45 was being constructed in the Houston Freeways book. you can download the book online here:

http://houstonfreeways.com/ebook.aspx

p147 in the gulf freeway section

Edited by gnu

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But traffic signals and traffic lights are supposed to give congested lanes greater priority, and it looks like that is what is happening in that picture. The difference between signals and circles is that one is supposed to do it by timer and one is supposed to do it automatically.

In which picture?

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I don't mind traffic circles much at all as long as they're not operating at above capacity. I've dealt with them all over Europe and they're usually fine and much more efficient than a stop sign or traffic signal when traffic is not too crazy. At less busy intersections they work well. At really busy intersections they don't work nearly as well. Also, true traffic circles, where all traffic entering the circle has to yield to traffic already in the cirlce works much better. A situation like what you have a Main, Montrose, and Hermann Dr. in the Museum District does not fit this model, because traffic on Montrose and Hermann Dr. has to come to a full stop to enter the circle, while traffic on Main yields to nobody. A design where everyone yields before entering the circle cuts down on a lot of the craziness because everyone has to slow down to enter the rotary. This is similar to how the Washington/Westcott roundabout that opened last year was built.

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There doesn't need to be an accident to produce this type of automotive logjam. Look carefully, and you would see that each direction's traffic flow is blocking another one. Kinda reminiscent of the Oppenheimer Funds logo. Look at the column of cars heading towards the top right of the picture. There is no way it can pass the solid wall of buses in front of it. This is basically the functional equivalent of a full dead-end, and when it gets bad, you have all four directions facing a dead end at the traffic circle intersection.

The greatest weakness of traffic circles is that through traffic has to negotiate with a hefty volume of crossing through traffic just to keep going straight. Four massive columns of solid through traffic are rarely able to smoothly progress past one another - it defies the physics of cars and the biology of human reactions. As mentioned above, the way around this is to augment high-capacity arterial intersections (such as this one in Xiamen, China) with grade-separated through lanes. That would be like Houston highway intersections (e.g., 1960/249) but with a traffic circle replacing the frontage road box. Driver courtesy (something altogether missing in China, I hear) would help as well - don't get in the way of other people if it doesn't get you anywhere.

Many folks misunderstand what modern roundabouts truly are. There is a difference between a modern roundabout and a traffic circle. The primary one being the yield-at-entry operation used in modern roundabouts. The picture you posted can happen in a traffic circle (because circulating traffic yields to entering traffic) but will not happen in a modern roundabout because the entering traffic must yield to traffic in the circle.

Modern roundabouts are not meant to be installed at every intersection in the world, but they can handle high volumes if properly designed and installed at the proper intersections.

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Many folks misunderstand what modern roundabouts truly are. There is a difference between a modern roundabout and a traffic circle. The primary one being the yield-at-entry operation used in modern roundabouts. The picture you posted can happen in a traffic circle (because circulating traffic yields to entering traffic) but will not happen in a modern roundabout because the entering traffic must yield to traffic in the circle.

if the roads exiting from the circle were backed up into the circle then i could understand the backup. but in this instance all the exiting roads are clear so that if the entering traffic is doing the yielding properly there wouldn't be this backup.

some of these look like they have 5 lanes trying to merge. i could see that being a nightmare just because of the sheer volume.

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It seems like a really good place for roundabouts are places like neighborhoods. When you're in a huge neighborhood, it can be a pain to stop at a million signs if you're heading towards the back.

So what kind of intersections would yall who seem to know more about this, suggest these things go if they were to implement them (which I think they are. I was on some city website and it had those listed as future projects)? Intersections that have mid-level congestion to lower level? Seems like yall think where there is a ton of congestion would be a bad place. Although in Paris at the Arc de Triumph, I believe that one has signal lights to help control flow, and although there were a ton of cars on there, it seemed to work pretty well, even though I was on foot and not in an automobile.

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if the roads exiting from the circle were backed up into the circle then i could understand the backup. but in this instance all the exiting roads are clear so that if the entering traffic is doing the yielding properly there wouldn't be this backup.

That's because the traffic circle in the photo is a traffic circle and not a roundabout. It isn't using yield at entry operation, hence the lockup.

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In the UK most roundabouts at major intersections have traffic signals to control the flow of traffic into the circle. There are occasional backups, but overall it seems to work fairly well. The confusing thing is being in the circle and having to maneuver to the correct lane to exit where you want, but at least traffic slows naturally as it enters the circle.

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It seems like a really good place for roundabouts are places like neighborhoods. When you're in a huge neighborhood, it can be a pain to stop at a million signs if you're heading towards the back.

So what kind of intersections would yall who seem to know more about this, suggest these things go if they were to implement them (which I think they are. I was on some city website and it had those listed as future projects)? Intersections that have mid-level congestion to lower level? Seems like yall think where there is a ton of congestion would be a bad place. Although in Paris at the Arc de Triumph, I believe that one has signal lights to help control flow, and although there were a ton of cars on there, it seemed to work pretty well, even though I was on foot and not in an automobile.

Personally, I think they are better suited for more suburban/rural settings, where traffic intensity is moderate, there are fewer pedestrians, and development is less dense. In those locales, they should be considered at unsignalized intersections before a signal is considered (although a signal may still be a better option for many intersections). While they usually cost more initially, they have essentially zero maintenance requirements and have an excellent safety record.

Edited by CDeb

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That's because the traffic circle in the photo is a traffic circle and not a roundabout. It isn't using yield at entry operation, hence the lockup.

concur

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concur

So what's the difference between a roundabout and a circle?

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So what's the difference between a roundabout and a circle?

There are three main differences:

1) The biggest is the operation. In traffic circles, the circulating traffic yields to entering traffic. In a roundabout, the entering traffic yields to the circulating traffic.

2) Size. Traffic circles are generally larger than roundabouts, thus having higher operating speeds and no safety advantage.

3) Flaring at entry. Roundabouts are more geometrically designed to slow enering vehicles, mainly by "flaring" the entry (i.e. adding curvature).

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Hmm. I thought they were just different names for the same thing.

Would that even work if the circulating traffic yields to entering traffic?

I have seen "mini-roundabouts" which are basically a dot painted in the street at an intersection. In these it seems strange having to yield to turning traffic when you are going straight.

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Hmm. I thought they were just different names for the same thing.

Common misconception. I believe that most people's aversion to roundabouts is due to their equating them with an awful traffic circle that they've experienced in the past.

And, as I've said before, roundabouts aren't a panacea. There are definitely some poorly-designed ones out there, and some installed at inappropriate locations.

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There was also another traffic circle on N. Wayside at Clinton Drive. Our high school student driving instructor made all of us drive this one and the one on Kelley St. (North Loop) at the Eastex Freeway. They were both pretty scary intersections for a 15 year old back in 1970. The driving instructor was a former marine sargent who was constantly barking at us to stay in our lane, keep your eyes on the road, to use our turn signals and so forth. Some of the girls would start to cry which really pissed him off even more. We all suvived though but those two traffic circles obviously didn't.

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I've seen photos of that one.

I guess your opinion depends on what you're used to. As it happens, I had a discussion about roundabouts last night with an English guy. He thought the worst thing about his experience driving in the US was the number of stop signs. He found it incredibly frustrating to go block after block starting and stopping, while with roundabouts you can frequently cover quite a distance without having to stopp. He also thought the system of stop signs and traffic signals was incredibly wasteful of fuel.

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Interesting stats on roundabouts from an NYTimes column.

Q. The United States has very few traffic circles, or roundabouts, as they are known in the United Kingdom. Are there traffic flow benefits to using traffic circles, assuming we could somehow teach the population how they should be properly entered and exited?

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I strongly oppose the use of unregulated traffic circles for arterial streets, as congestion in one direction can obstruct traffic going in the other three directions. The most problematic thoroughfares, such as SH6, need overpasses. However, traffic circles in residential neighbourhoods would be greatly beneficial, as an alternative to frequent stop signs.

Well said. My native country uses rotary style a lot, even on busy streets. Guess what? Traffic is nerve-racking-everyday of the week.

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I just got back from Cairns, Australia. They have a ton of giant traffic circles. Traffic definitely seems to flow faster and it cuts down on commute times, but as the original post says, it is a nightmare for pedestrians. You can't tell which cars are going to be coming your way and during rush hour the cars come constantly.

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At busy traffic circles in large cities in Europe, there are usually pedestrian tunnels or pedestrian signals to allow pedestrians to navigate the intersection safely. Several of these also exist with at circles in Washington DC.

I'm all for increased use of yield-entry modern traffic circles in this country. Several states are using them more often, such as Colorado, and they work quite well. There's one in Grand Junction I drive through on a daily basis when I'm there for work, and it is much easier than dealing with a traffic light, especially since my morning commute always involves a left turn at this particular intersection.

The idea that people would find it difficult to go slowly around a small circle with other cars raises questions about whether those people should be operating heavy machinery to begin with.

This is so true! Of course these idiots who can't understand a roundabout are the same ones who can't understand a no left turn sign on Main St. in Houston.

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Doha, Qatar is removeing most of the roundabouts, or putting signals on the ones where streets enter at odd angles. Removing the roundabouts has helped traffic flow tremendously, and prevented many accidents caused by drivers not following the rules on how to enter and leave roundabouts. Removal is pretty easy, as there's plent of space to put in multiple left turn lanes while maintaining the same number of through lanes.

Edited by Ross

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Doha, Qatar is removeing most of the roundabouts, or putting signals on the ones where streets enter at odd angles. Removing the roundabouts has helped traffic flow tremendously, and prevented many accidents caused by drivers not following the rules on how to enter and leave roundabouts. Removal is pretty easy, as there's plent of space to put in multiple left turn lanes while maintaining the same number of through lanes.

Dubai is also replacing congested roundabouts with standard four-way intersections. For example, the roundabout at Sheikh Kalifa bin Zayed Street and Bin Al Waleed Street in front of the Burjuman: it might have been a great idea fifteen years ago, when the number of vehicles in Dubai was a fraction of what they are today, but today that intersection is an absolute disaster. Once construction on the metro station at that location is complete, the roundabout will be replaced with a conventional intersection.

Roundabouts that haven't yet become congested, on the other hand, seem to work well.

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I agree. From what I've seen there are almost never roundabouts in congested city where there is a lot of pedestrian traffic. In pedestrian areas of cities it seems better to have signalized intersections to allow safe pedestrian crossing. On the other hand, small roundabouts in low traffic residential neighborhoods can be OK for pedestrians, since they are about the same size as an intersection with a stop sign (just paint a white dot in the middle).

What can be a challenge is riding a bicycle through a circle. This is because bikers generally keep to the side, and in a roundabout drivers will assume you plan to turn our of the circle and cut you off. I had several near-misses from this happening until a bike-commuting colleague pointed out that the trick was to cut closer into the center of the circle which will force cars to yield. I do that now and it works just fine. So now you know. ^_^

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What can be a challenge is riding a bicycle through a circle. This is because bikers generally keep to the side, and in a roundabout drivers will assume you plan to turn our of the circle and cut you off. I had several near-misses from this happening until a bike-commuting colleague pointed out that the trick was to cut closer into the center of the circle which will force cars to yield. I do that now and it works just fine. So now you know. ^_^

What you're saying makes sense.

Sense doesn't seem to be overrepresented among Houston drivers. I fear that nothing less than bicycles equipped with mine-like explosives will 'force' anyone to yield, locally.

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Learning to love the roundabout!

Why American drivers should learn to love the roundabout.

By Tom VanderbiltPosted Monday, July 20, 2009, at 6:54 AM ET

Here is a narrative that has been playing out over the last several years in any number of American towns: Traffic engineers notice that a particular intersection has a crash problem or is moving traffic inefficiently. After a period of study, the engineers propose a roundabout. The engineers, armed with drawings and PowerPoint slides, visit a community meeting. They try to explain the benefits of their proposed design in clear language, though they may occasionally drop phrases like entry path overlap or inscribed circle diameter. Townspeople raise concerns. Roundabouts are not safe, they say. They are confusing. They are bad for pedestrians. They will hurt local businesses. They are more expensive than traditional solutions. The local newspaper reports this, adding some man-in-the-street comments from "area drivers," who profess not to like roundabouts, even making dark references to "circles of death." Then, the roundabout is built, the safety record improves, traffic congestion doesn't seem any worse than before, and the complaints begin to fade faster than white thermoplastic lane markings in the heat of summer.

According to best estimates, the United States is now home to about 2,000 "modern roundabouts"—more on that phrase in a moment—most of which were built in the last decade. As engineer Ken Sides noted in the ITE Journal, however, in 2008 Australia built its 8,000th roundabout; by Sides' calculation, the United States would need to build roughly 148,519 more roundabouts to match the Australian rate per capita. Interestingly, Australia—a country whose traffic landscape is rather similar to ours—has, since 1980, cut its traffic-fatality rate to nearly half the U.S. figure. The rise of roundabouts has no doubt played some part.

Why are Americans so suspicious of roundabouts? The simplest answer is that we have grown used to (and feel comfortable with) binary, on-off traffic control. We suspect such signals are more efficient than the "fuzzy logic" that seems to govern roundabouts. Roundabouts require drivers to make their own decisions and assess others' actions, rather than relying on third-party signals.

And here is the link..

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I was in Sedona, AZ recently, where they replaced a few intersections along hwys 179 & 89 with roundabouts just under a year ago. They're at intersections where the major thoroughfare through the town is a state hwy, with small cross streets. Apparently they've been pretty effective at reducing congestion.

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