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Old 04-15-2011, 11:39 AM
 
443 posts, read 536,282 times
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The first SPUI was built in Clearwater FL at the intersection of US 19 and FL 60 in 1970.

The first DDI was built in Versailles France in 1975.
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Old 04-15-2011, 12:04 PM
 
443 posts, read 536,282 times
Reputation: 176
[quote=neil0311;13411481]NOOOOoooooooo. Having lived in New England where "rotaries" are rampant, I can tell you that they are NOT a benefit to traffic, and cause delays. I used to sit in traffic at the one in Concord, MA daily for years. In fact, a famous rotary on Cape Cod at the Sagamore Bridge was recently removed to allow better traffic flow. The backups on summer weekends at that rotary were legendary.

There are differences between the old "traffic circle" and the modern roundabout:

1. On the traffic circle, they usually designated one street to be the priority road, and the connections to the other street (including the left turns on the circle) had to stop. these stops locked up the circle.

On the roundabout, entering traffic has to yield to traffic already in the circle. Problem solved.

2. On the traffic circle, emphasis was often on merging. There is no merging on the roundabout.

3. The traffic circle was often large, with weaving areas between legs. There is no weaving on the roundabout. It is illegal to change lanes or overtake other cars within the circle of a roundabout.

4. You choose your lane before you enter the roundabout.
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Old 04-15-2011, 12:17 PM
 
Location: Atlanta
6,645 posts, read 8,115,993 times
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Quote:
Originally Posted by neil0311 View Post
NOOOOoooooooo. Having lived in New England where "rotaries" are rampant, I can tell you that they are NOT a benefit to traffic, and cause delays. I used to sit in traffic at the one in Concord, MA daily for years. In fact, a famous rotary on Cape Cod at the Sagamore Bridge was recently removed to allow better traffic flow. The backups on summer weekends at that rotary were legendary.

Boston.com / News / Local / Mass. / State OK's removal of Sagamore rotary
They are actually cheaper and more effective....

The catch is they are that way for roads with less traffic than you would typically see on a major 4+ lane road.

Think of it more as a replacement for 4-ways tops and slightly busier traffic light intersections on intersecting 2-lane roads and less used 4 lane roads.

They can handle more cars throughout the day, since traffic never has to fully stop.

I think the trick is the differentiate the difference between a roundabout and a traffic circle. Most people here roundabout and think traffic circle.

The GDOT is pushing them along with many other states, like Minnesota that was mentioned.

If anyone wants to exmaing GDOT's stance and design guide on them ... go here

Roundabouts

Look in the presentations. The GDOT requires the intersection handles less than 25,000 cars/day and the major road has less than 90% of the traffic using the intersection.

For a multilane road it is less than 45,000 cars/day.

I can think of a handful of heavily used 4-ways tops these would be good at replacing and a handful of traffic light intersections these could replace in Gwinnett.

The major thoroughfares in my neck of the woods like US29, US78, and Indian Trail/Killian Hill Rd would never be touched as they have too many cars.
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Old 04-15-2011, 12:26 PM
 
Location: Atlanta
6,645 posts, read 8,115,993 times
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SPUI

Lenox
Atlanta, ga - Google Maps
Sugarloaf extension
Atlanta, ga - Google Maps
PBI
Atlanta, ga - Google Maps
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Old 04-15-2011, 01:10 PM
 
Location: Marietta, GA
7,862 posts, read 15,285,591 times
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Quote:
Originally Posted by cwkimbro View Post
They are actually cheaper and more effective....

The catch is they are that way for roads with less traffic than you would typically see on a major 4+ lane road.

Think of it more as a replacement for 4-ways tops and slightly busier traffic light intersections on intersecting 2-lane roads and less used 4 lane roads.

They can handle more cars throughout the day, since traffic never has to fully stop.

I think the trick is the differentiate the difference between a roundabout and a traffic circle. Most people here roundabout and think traffic circle.

The GDOT is pushing them along with many other states, like Minnesota that was mentioned.

If anyone wants to exmaing GDOT's stance and design guide on them ... go here

Roundabouts

Look in the presentations. The GDOT requires the intersection handles less than 25,000 cars/day and the major road has less than 90% of the traffic using the intersection.

For a multilane road it is less than 45,000 cars/day.

I can think of a handful of heavily used 4-ways tops these would be good at replacing and a handful of traffic light intersections these could replace in Gwinnett.

The major thoroughfares in my neck of the woods like US29, US78, and Indian Trail/Killian Hill Rd would never be touched as they have too many cars.
Sorry, but having lived in New England for 15 years where large rotaries on major roads are a fact of life, and having heard the discussions around removing rotaries from Massachusetts roads, you're wrong, at least as the facts apply in urban areas like Boston and in heavy traffic areas like the Sagamore bridge.

I'm sure that on some country road in the middle of nowhere, rotaries may be a better and less expensive option, but not in heavily traveled urban and suburban areas.

Anyone else from New England want to weigh in on the "benefits" of rotaries?
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Old 04-15-2011, 04:03 PM
 
Location: Atlanta
6,645 posts, read 8,115,993 times
Reputation: 4511
Quote:
Originally Posted by neil0311 View Post
Sorry, but having lived in New England for 15 years where large rotaries on major roads are a fact of life, and having heard the discussions around removing rotaries from Massachusetts roads, you're wrong, at least as the facts apply in urban areas like Boston and in heavy traffic areas like the Sagamore bridge.

I'm sure that on some country road in the middle of nowhere, rotaries may be a better and less expensive option, but not in heavily traveled urban and suburban areas.

Anyone else from New England want to weigh in on the "benefits" of rotaries?
Well thank you for your opinion. If your opinion feels that way, then clearly I must be wrong...

I have seen them implemented and used very well in many places. When I look over GDOT's design and implementation documentation I feel that their heads are in the right places.

The rotary to mentioned before wasn't a traditional roundabout by modern traffic standards it often had up to 70,000 cars/day, which is way above design guidelines. Correct me if I am wrong on this, but I think it was replaced with a full grade separated interchange. That is not a good example of what a roundabout is, is about, or how it should be used and implemented.

I have used them right here in Georgia, as well as in Germany and France when I travel their for work quite often.... and I have to say when appropriately installed they work really well and often increase intersection capacity over that of a basic traditional 4-way stop or simple lighted intersection.

Now if the intersection capacity is too high, then we have to look for other strategies, like grade separations, medians, dual left turn lanes, right turn lanes, ITS corridor light timing, etc... However, we only do that to high capacity intersections and thoroughfares, which wouldn't match the design guidelines for a roundabout.
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Old 04-16-2011, 12:28 PM
 
443 posts, read 536,282 times
Reputation: 176
Quote:
Originally Posted by neil0311 View Post
Sorry, but having lived in New England for 15 years where large rotaries on major roads are a fact of life, and having heard the discussions around removing rotaries from Massachusetts roads, you're wrong, at least as the facts apply in urban areas like Boston and in heavy traffic areas like the Sagamore bridge.

I'm sure that on some country road in the middle of nowhere, rotaries may be a better and less expensive option, but not in heavily traveled urban and suburban areas.

Anyone else from New England want to weigh in on the "benefits" of rotaries?
Roundabouts are not the same as the old rotaries (traffic circles).

The old rotaries were designed using the wrong methods. They failed becaused they expected drivers to weave. Changing lanes while traveling on a curve is very hard to do. It caused accidents and locked up the rotary.

No weaving takes place on a roundabout. Yielding occurs when entering the roundabout. All lane changing is done before entering the roundabout. It is illegal to change lanes while on the circular roadway of a roundabout.

A roundabout can not lock up, unless one of the downstream exits backs up for other reasons. The only time I ever saw one lock up was when a huge event at a church caused traffic waiting to turn left into the parking lot to back up into the roundabout. Posting a policeman at the driveway to direct traffic fixed the problem. On the other hand, I often drive on a rotary in a nearby town, and it constantly locks up because of its bad design.

A rotary can be changed into a roundabout with the following modifications:

- Reduce the size of the rotary and central island to the point where no weaving can take place.

- Remove anything tall from the central island. Drivers must be able to see all of the traffic.

- Require all entering traffic to yield to traffic already on the circular roadway. No road has priority over another road at a roundabout.

- Prohibit passing, lane changing, and entering alongside a circulating car. The driver must stay in his lane throughout the passage through the roundabout.

- Require drivers to get in the correct lane before entering the roundabout. The markings will then correctly direct him to his exit.
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Old 04-16-2011, 12:58 PM
 
Location: Marietta, GA
7,862 posts, read 15,285,591 times
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Originally Posted by cwkimbro View Post
Well thank you for your opinion. If your opinion feels that way, then clearly I must be wrong...
Thanks for your sarcasm.

No...the Commonwealth of Massachusetts also thinks you're wrong, and my response was qualified. In low volume roads in Europe and places in the US, they may be fine. They are not in heavily trafficked urban areas like Boston and Atlanta.

As I stated in my previous response earlier in the thread, the other given about rotaries is that drivers have to be able to use them and understand what to do. Drivers in Georgia do not. They can barely drive on roads as they exist now, let alone with the addition of a traffic flow pattern that is utterly foreign to them.

I can see it now...indecisive people sitting and waiting for every car for a mile to disappear before they venture out into the rotary. Other people cutting off drivers in the rotary, and the rest of us being held up by the idiots. Hell, we can't even get people today to go around left turning cars or make a left turn when they have the opening. A rotary in heavy traffic with southern drivers would be a disaster.
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Old 04-16-2011, 03:40 PM
 
Location: Atlanta
6,645 posts, read 8,115,993 times
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Quote:
Originally Posted by neil0311 View Post
Thanks for your sarcasm.

No...the Commonwealth of Massachusetts also thinks you're wrong, and my response was qualified. In low volume roads in Europe and places in the US, they may be fine. They are not in heavily trafficked urban areas like Boston and Atlanta.

As I stated in my previous response earlier in the thread, the other given about rotaries is that drivers have to be able to use them and understand what to do. Drivers in Georgia do not. They can barely drive on roads as they exist now, let alone with the addition of a traffic flow pattern that is utterly foreign to them.

I can see it now...indecisive people sitting and waiting for every car for a mile to disappear before they venture out into the rotary. Other people cutting off drivers in the rotary, and the rest of us being held up by the idiots. Hell, we can't even get people today to go around left turning cars or make a left turn when they have the opening. A rotary in heavy traffic with southern drivers would be a disaster.
Ahh well clearly if the commonwealth of Massachusetts think I am wrong... I must be wrong. Clearly... they do everything in exactly the only one true right way to do things


Neil, here is the issue... you need to read and consider my opinions and those of others in their entirety.

You may not agree, but no one is arguing we should make large traffic circles or place these on our highest volume roads. Yet, all of your counterarguments keep referring to that.... the highest volume roads.

The other thing that needs to be considered.... in case anyone hasn't noticed Metro Atlanta is full of two lane roads that only see low and moderate amounts of traffic. Most traffic is funneled onto larger state and federal roads to cross county lines. We have tons of 4-way stops and traffic lights at low and moderate volume intersections that can back up traffic from design limitations and increase safety problems from the turning patterns of the intersection.

These roads are often given lots of different names, like a secondary road, a local artery, or a collector street. And they all have the same problem with they intersect.

Take the time to look over the design guidelines and their implementation and get the idea of traffic circles and rotaries out of your head....this isn't to ignore the failures that can be found in other places, but it instead to look at what people actually are referring to as a roundabout and to take the ideas that have been successfully implemented in other places.

You may disagree and that is fine, but most people don't take too kindly to being told they are wrong when their ideas actually have some merits worth considering and there ideas are compared to other failures that have just about nothing to do with the purpose of the original idea.

An intersection carrying 70,000 cars/day in a large traffic circle is not a roundabout. Nor would that meet the design guidelines in all of the states beginning to test and implement them.

For anyone else interested.... roundabouts are being encouraged and implemented by the Federal Highway Administration and state DOTs across the country are slowly beginning to implement and test them.
When used under the prescribed design guidelines given by the FHWA and state DOTs as designed from academic civil engineers they have increased traffic flow, decreased the number of wrecks in an intersection, and more importantly decreased the severity of an accident when they do occur.

The state DOT page as a good deal of information about them as well as a list of where they are implemented. It is a good read for anyone interested. Roundabouts

There are a few examples in GA, but admittedly not many. A word of caution... a few of the roundabouts constructed by -local- governments on local government funded roads do not necessarily meet the proper design guidelines. In these situations they have some of the benefits, but can also have some problems.

Here is one test example in Gwinnett that I have seen in my part of town. Atlanta, ga - Google Maps
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Old 04-16-2011, 07:51 PM
 
Location: Marietta, GA
7,862 posts, read 15,285,591 times
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Quote:
Originally Posted by cwkimbro View Post
Ahh well clearly if the commonwealth of Massachusetts think I am wrong... I must be wrong. Clearly... they do everything in exactly the only one true right way to do things
Yes, because you obviously have more experience than professional traffic engineers who live with this issue. Think I'm done with this thread, as I obviously have nothing more to offer.
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