Rotaries, Roundabouts, and Traffic Circles

[Witch King]

... but I wouldn't be surprised if they went back and added road humps as well.

Here's a proper roundabout in Houston...

http://maps.google.c...004823&t=h&z=18

They did.

[samagon]

Most of the high traffic roundabouts I've seen in England have traffic lights, it's not a free-for-all. Those are usually just on smaller roads. A roundabout with lights is still useful, it allows for new traffic to start going well before the previous traffic exits the intersection.

absolutely, whether the intersection is metered through use of traffic lights, or signs, they are still safer, cause when you enter the traffic circle, you should only have to look for cars coming from the left.

[Subdude]

Roundabouts on the move! from today's Economist:

 

 

 

First introduced in Letchworth Garden City in 1909, the roundabout—a one-way gyratory built for road management not to circumvent a monument—proved so popular in Britain that in the 1960s the Transport Research Laboratory developed a miniature version. It reached its apogee in Swindon’s “Magic Roundabout” (pictured): one large roundabout surrounded by five mini satellites. The UK Roundabout Appreciation Society celebrates this gyratory ballet on a set of exclusive place mats. The society’s coveted “Best Roundabout of the Year” title is currently held by one in York with a windmill on it, which beat a rival with a duck-pond in a closely fought contest.

As so often happens, others are following where Britain led. In 1997 there were 30,000-40,000 roundabouts around the world; now there are 60,000. Half of them are in France: the French were early converts to the rond-point and have taken to it with a passion, perhaps because it offers conspicuous opportunities for the country’s notoriously competitive municipal gardeners to vie with neighbouring rivals. America is catching up fast; numbers have grown from a few hundred to 3,000 in the past decade. They are now common across Europe and have spread from the rich world to the developing one (see article).

 

 

[Slick Vik]

The city my dad is from is full of roundabouts. I've seen people get stuck in them for 30-40 minutes.

[Naviguessor]

A Traffic circle at Navigation/Runnels/Jensen would be perfect...would give the area a unique, and effective, entry point...and keep traffic moving.   The Lights at Canal and Navigation drive me crazy.

[Ross]

Most of the roundabouts in Doha, Qatar have been removed in favor of regular light controlled intersections. The roundabouts were fine when traffic was light, but became bottlenecks as traffic grew.

 

 

[Slick Vik]

Most of the roundabouts in Doha, Qatar have been removed in favor of regular light controlled intersections. The roundabouts were fine when traffic was light, but became bottlenecks as traffic grew.

I agree you can get stuck for long periods of time in them.

[livincinco]

Most of the roundabouts in Doha, Qatar have been removed in favor of regular light controlled intersections. The roundabouts were fine when traffic was light, but became bottlenecks as traffic grew.

Surprised that they didn't just introduce traffic lights to the roundabouts. They can be pretty efficient in high traffic situations once that is done.

[Ross]

Surprised that they didn't just introduce traffic lights to the roundabouts. They can be pretty efficient in high traffic situations once that is done.

 

A lot of the roundabouts were for right angle intersections, or where a side street came into a main arterial. Lights definitely work better for those. They have lights on roundabouts where the angles are weird, or where there's more than 4 roads coming in.

 

[Fringe]

I just recently visited the New England area for the first time. Traffic circles EVERYWHERE. (Or roundabouts, whatever you want to call them). Seemed to be working up there but not sure about down here. 

[livincinco]

I just recently visited the New England area for the first time. Traffic circles EVERYWHERE. (Or roundabouts, whatever you want to call them). Seemed to be working up there but not sure about down here.

Speaking of New England, I have no problem with traffic circles, but those little left turns in New Jersey need to be condemned to some obscure level of h$ll.

[august948]

Some genius developer put two roundabouts in ordinary intersections in a neighborhood on Benignus Rd just west of Memorial City.

[Slick Vik]

Some genius developer put two roundabouts in ordinary intersections in a neighborhood on Benignus Rd just west of Memorial City.

I went to park city a couple of weeks ago and it was full of roundabouts.

[livincinco]

That's more about wanting Park City to feel "European" than it is about managing traffic flow.

[innerloop]

I go through the one at Washington/Westcott fairly often and I'm surprised that it is working well.  I've always liked roundabouts since I was a kid growing up and my family would get to drive on the one down in front of the Warwick when we were going to the zoo.  Now that I live in the Heights I'm campaigning for one at the intersection of Studewood/Main/Cavalcade/20th.

[Subdude]

Surprised that they didn't just introduce traffic lights to the roundabouts. They can be pretty efficient in high traffic situations once that is done.

 

I think part of the trick also is scaling the size to the amount of traffic.  I've seen a number of small low-traffic intersections that were basically circles painted on the ground, but when it gets to larger arteries they have to be scaled up proportionately. 

 

 

 

 

I just recently visited the New England area for the first time. Traffic circles EVERYWHERE. (Or roundabouts, whatever you want to call them). 

 

Which brings up a question on terminology.  To me it seems I've heard "roundabout" most often.  Is "traffic circle" more of a New England / Northern expression?

[IronTiger]

Wikipedia has them as different things, so they must have SOME differentiation. Me? I don't like traffic circles or roundabouts, unless certain criteria are met:

 

1. A road angles at a sharp 90° turn, which would otherwise require a stop and then a left turn.

2. A road breaks into two and it would be easier than an awkward Y-shaped intersection.

3. The joining road has one lane in each direction, or if not, the total traffic on the intersection is very low.

4. The road isn't reconfigured from a traditional stoplight.

5. The traffic circle, if replacing a traditional stoplight, eliminates not one, but two lights.

6. No property is forced to be condemned for the construction (relates to #4)

7. It was built before 1970 (thus, grandfathered in)

 

Traffic circles require a lot of extra land, so they're not practical in some circumstances. Some trucks may not be able to make the tighter curves a roundabout forces and often requires a lot of curb driving.

 

However, if you notice the criteria I have outlined, it doesn't eliminate all traffic circles or roundabouts from existence, it just gets rid of the more annoying ones. 

 

 

[IronTiger]

Additionally, I would like to amend my list:

8. The traffic circle would reduce traffic by a dramatic amount (improve traffic flow by 300%, or something cool), which couldn't be achieved through other means (such as timing lights better). This would negate #4 or even #6...but I doubt it.

 

[skooljunkie]

I often wish all three signals at the Ella/W. T. C. Jester/W. 18th intersections would be removed and replaced with a roundabout.  It would be kind of cool if the Jack in the Box could be salvaged and left in the middle.

[ig2ba]

I go through the one at Washington/Westcott fairly often and I'm surprised that it is working well.  I've always liked roundabouts since I was a kid growing up and my family would get to drive on the one down in front of the Warwick when we were going to the zoo.  Now that I live in the Heights I'm campaigning for one at the intersection of Studewood/Main/Cavalcade/20th.

 

The Washington-Westcott rotary always struck me as too small for optimum function. There's only about a car length between some entrances to the next exit (1. SB Westcott to Arnot, 2. NB Westcott to Washington, 3. WB Washington to NB Westcott), so there's obviously no room for cars to weave and change places - cars instead just have to wait on the outside of the rotary, and this is not the intent of a rotary.

 

They also seem a lot smaller than I'm used to seeing. I took a look at about 25 rotaries in the Boston area. With the exception of one which ends in on street parking at the beach (in Revere), every single one of them that I looked at had an inner radius of 175-200+ feet, and an outer radius of 275+ feet. Most were larger than that, and very few were town squares or similar, but just rotary islands. The larger size gives cars more time to maneuver in and out. Think of it as the difference between short merge lanes on the freeway (e.g., https://maps.google.com/?ll=29.758807,-95.374585&spn=0.000005,0.002401&t=m&z=19&layer=c&cbll=29.758807,-95.374585&panoid=4IKpqYWzmQ1L3B1DBldqOw&cbp=12,187.89,,0,18.6) vs. modern, longer ones (https://maps.google.com/?ll=29.987864,-95.423384&spn=0.000019,0.009602&t=m&z=17&layer=c&cbll=29.988005,-95.423425&panoid=Zj0FRdC3TV8nsO52Bk-zOw&cbp=12,12.31,,0,16.09)

 

The Washington-Westcott rotary is only 120 feet inner, 180 feet outer radius. And this is the best-functioning roundabout in Houston. The ones on Benignus are little more than glorified speed bumps; that's okay with me though, and my car's suspension is also thankful.

 

If we build any more in Houston and expect to get any benefits other than aesthetic or glorified speedbumps, let's do it right next time. I started out writing, not even looking at your Heights example, but now that I look at it, I question whether it would work effectively without taking through eminent domain. It would be even smaller than the W/W one, and I don't see how it would work, especially since all 5 streets are busy vs. only 4 in the W/W rotary.

 

Edit: It seems like perimeter of the rotary might be a more important measure than it's radius, since merging distance is the important factor. So, it doesn't have to be a perfect circle, and oblong ones might be more effective.

[IronTiger]

And that would violate #6 of my list...condemning property...

[ig2ba]

I often wish all three signals at the Ella/W. T. C. Jester/W. 18th intersections would be removed and replaced with a roundabout.  It would be kind of cool if the Jack in the Box could be salvaged and left in the middle.

 

Interesting idea. If the Jack in the Box were to be kept, I think it would have to have only one exit and one entrance, which it currently does not have.

[august948]

Roundabouts on the move! from today's Economist:

 

 

 

Holy cr@p!  If I ever ran into something like that I think I'd just stop my car and run far, far away.

 

[ig2ba]

Holy cr@p!  If I ever ran into something like that I think I'd just stop my car and run far, far away.

 

I know people who have that same feeling when they come to Houston. Especially those from other countries. They've never seen freeways anything like ours before.

[Subdude]

Holy cr@p!  If I ever ran into something like that I think I'd just stop my car and run far, far away.

 

In a previous existence I briefly had an apartment right up the street from this roundabout, but I still went to some pains to bypass it since I could never seem to quite conceptualize the logic of the thing.  Nevertheless occasionally it was unavoidable, but I finally figured out the best way to navigate it was to clench the wheel and just follow other drivers who presumably knew what they were doing. 

 

Hence perhaps my interest in roundabouts as a sort of all-purpose traffic solution.

 

 

[JamesL]

The Washington-Westcott rotary always struck me as too small for optimum function. 

 

 

 

It is too small for a rotary because it's not a rotary. It's a roundabout. Roundabouts are designed to control speed. Traffic is supposed to yield on antry and there should be no lane changes once in the roundabout.