Talk:Roundabout

Hamburger Roundabout

There is an example here (Perth, Western Australia. Morley Drive (east-west), Alexander Drive (north-south), The Strand (NW-SE). The existing roundabout was bisected some time in the 1980's. --michael 07:03, 6 May 2006 (UTC)

There is an example here in Fairfax, VA, US, at the intersection of US 29/VA 237 Lee Hwy, US 50 Fairfax Blvd, US 29/50 Fairfax Blvd, and Old Lee Hwy. US 50 goes through the circle, US 29 goes partway through the circle, and VA 237 the goes around it. séain (talk) 02:47, 21 August 2008 (UTC)

capacity vs conventional intersections

"Roundabouts are not suitable for junctions where the exits suffer from traffic congestion. Congestion on one exit commonly blocks a roundabout and spreads to all entering directions. " All intersections suffer if spillback from an adjacent intersection extends through them. Why make a special point about it for roundabouts? --Triskele Jim 16:36, 29 October 2007 (UTC)

OK. Paragraph removed to here -- together with adjunct about Kwai Tsing Interchange since that is uncited.--Farry 19:55, 12 November 2007 (UTC)

"Roundabouts are not suitable for junctions where the exits suffer from traffic congestion. Congestion on one exit commonly blocks a roundabout and spreads to all entering directions. The roundabout of Kwai Tsing Interchange in Hong Kong was replaced by a large box junction with traffic lights after recurring area traffic congestion when numerous container trucks journeyed to Kwai Chung Container Port after a typhoon."

I think the point is that if a signalized intersection has more volume than capacity, then traffic backs up and you start queing, LOS F and more... ...but the intersection still 'works.' When a roundabout has more volume than capacity at the exits, and the queues back up, the roundabout is typically 'paralyzed' with no movement anywhere; maybe only between adjacent exits with multi lane roundabouts.Wvfd14 (talk) 12:28, 20 May 2008 (UTC)

A yield-on-entry roundabout will continue to flow when over capacity, perhaps better than a signal, since ther is no lost time for phase changes. Roundabouts almost always have more capacity at the exits than the entrances. Problems occur when the next downstream intersection backs up through the roundabout, but this hurts all types of intersections.

A separate problem is traffic circles where circulating traffic must yield to entering traffic. These will gridlock themselves.Triskele Jim (talk) 17:09, 20 May 2008 (UTC)

Does the fact that these two images show driving on the right reflect some bias? The intersection example is an oversimplification, because the left turners don't cross each other's path, but they certainly have to cross any straight-through traffic, which would have the right of way. The advantage of the roundabout is that straight-through traffic does not impede the left turner (in a driving on the right example). Roundabouts become congested when there is one dominant stream making a 270 degree turn, such as at rush hour. Traffic still moves freely on the roundabout, but only in the dominant stream, and drivers at the intermediate entrances find it hard to break in. This situation is easily cured by the signalized roundabout, which can force gaps in the dominant stream.24.108.87.94 (talk) 23:14, 27 December 2008 (UTC)

"Roundabouts and cyclists" section

The subheadings should be merged, because their subjects overlap and there are several repeating sentences. Admiral Norton ^(talk) 20:45, 24 February 2008 (UTC)

I disagree. Cyclists and pedestrians have quite different needs and characteristics. This is especially true at roundabouts. Pedestrians are often safer at roundabouts, but cyclists often run into problems, especially at multi-lane roundabouts. Perhaps these sections could be re-written, but I don't think they should be merged. —Preceding unsigned comment added by Triskele Jim (talk • contribs) 20:46, 25 February 2008 (UTC)

Turbo roundabouts

I've added a stub for turbo roundabouts, and an image showing one schematically. English is not my native language, so my contribution will probably need some editing. See also http://nl.wikipedia.org/wiki/Turborotonde. 82.95.131.38 (talk) 23:29, 11 April 2008 (UTC)

Wow... that looks almost intentionally evil. I'm confused as to how it's supposed to work effectively, except for people turning left (and then only a slight improvement). For one thing it appears to give you a different flexibility of travel direction depending on whether you're north/south or east/west - or is that just an artist error? 193.63.174.210 (talk) 19:56, 17 November 2008 (UTC)

I'm confused you are saying it's evil. I don't understand that. In the Netherlands we now have almost 80 turbo roundabouts and the number is still increasing. One-lane roundabouts do not have a high capacity. So that is why two-lane roundabouts are being build. Two-lane roundabouts have a higher capacity but also lower road safety compared to one-lane roundabouts due to the higher speed and the risk of wrong lane changing. A turbo roundabout has a higher capacity than an one-lane roundabout but it has the same traffic safety. If you have any questions feel free to ask them. For pictures of the Dutch turbo see this pdf especially page 5. http://www.royalhaskoning.com/NR/rdonlyres/6EB9E06A-6846-4B3E-B4DD-2528675E78F6/0/Turborotondes.pdf 83.82.185.13 (talk) 17:18, 3 December 2008 (UTC)

It looks worse in plan view than it does to the driver. Print it out, lay it near the edge of a table, then look at it from a flat angel while kneeling next to the table. Then I think you'll see that, if properly designed and signed, they actually make sense.--Triskele Jim (talk) 17:34, 3 December 2008 (UTC)

Pedestrians?

Since when have pedestrians usually been banned from the middle of roundabouts? I've come across many roundabouts where it's common to cross the the center island, then to the destination road - particularly with many exits. On larger roundabouts it's common for the middle to be unsuitable, ie no pavements (sidewalks), walls, etc, but that's not the same as saying pedestrians are prohibited from there. Smaller ones less so. 128.232.228.174 (talk) 13:53, 13 May 2008 (UTC)

Pedestrians have been (usually) banned from modern roundabouts since forever. The top of the article has a list of differences between roundabouts and traffic circles. If a roundabout allows pedestrian traffic into the middle then it is usually a traffic circle.

from Roundabouts: An Informational Guide[1]:

2.2.1 Pedestrians

Pedestrians are accommodated by crossings around the perimeter of the roundabout. By providing space to pause on the splitter island, pedestrians can consider one direction of conflicting traffic at a time, which simplifies the task of crossing the street. The roundabout should be designed to discourage pedestrians from crossing to the central island, e.g., with landscape buffers on the corners. Pedestrian crossings are set back from the yield line by one or more vehicle lengths to:
• Shorten the crossing distance compared to locations adjacent to the inscribed circle;
• Separate vehicle-vehicle and vehicle-pedestrian conflict points; and

• Allow the second entering driver to devote full attention to crossing pedestrians

So, pedestrians are "banned" from the center island in modern roundabouts.Wvfd14 (talk) 16:43, 13 May 2008 (UTC)

No pedestrian access to the central island is the phrase used in the FHWA: Roundabouts an Informational Guide, guidebook.

I think a bigger issue related to pedestrians is the pending access board decision to require signalized pedestrian crossings at all multi-lane roundabouts where pedestrian facilities are provided. This would largely increase the cost of roundabouts, and make roundabouts tougher to justify. —Preceding unsigned comment added by 63.90.172.36 (talk) 15:08, 4 June 2008 (UTC)

Cornish Double Roudabouts

I think these curious aberrations would be worthy of mention, if anyone could explain the Cornish road planners' predilection for them. Bill F (talk) 22:07, 18 May 2008 (UTC)

I assume you are referring to some type of roadway geometry in the Cornwall region of Britain? I assume you mean something like this, but in the future I recommend that you provide examples. Also it sounds like you may have a personal gripe with them... please keep in mind WP:NPOV. I would expect that the engineers & planners that installed them had a good reason; and they likely continue to have a good reason considering that they are still there. --Bossi (talk • gallery • contrib) 23:05, 18 May 2008 (UTC)

I don't think a conventional roundabout would fit in the location shown in Bossi's example, without taking the buildings on the northeast and southwest corners.Triskele Jim (talk) 17:14, 20 May 2008 (UTC)

The two circles could be merged to form an oval; this would make right-turns onto Fore Street longer, for little benefit that I can see. —Tamfang (talk) 06:09, 29 August 2008 (UTC)

Bossi, Cornwall is an English county, not a region. Your example does show what I am talking about. I do not need instruction on POV, thank you. Planners often have reasons, but not invariably good ones. How do you know the planners in question have not been fired? If references showed that some type of traffic control system were the subject of widespread opprobrium, would that not be legitimate article content? A merest tinge of humour in a talk page can occasionally help things along.

Triskele Jim, If there are space restrictions, I think you will find a single mini-roundabout is the more usual British solution. Bill F (talk) 23:08, 22 May 2008 (UTC)

I think this is meant with a mind towards where it would be beneficial to replace a simple staggered, oblique, multiple or otherwise complex intersection with a more controlled and equal-flow solution where the money isn't available to install and run traffic lights, but there isn't the space available (or again, the cash) to make the British Road Designer's favourite lazy-arse solution of whacking in a simple perfectly circular island big enough to allow all the connected roads to hit it in a roughly perpendicular manner with the minimum of other re-engineering. The alternative is a single wierdly-shaped roundabout, and this will have both lower overall capacity (for the same reasons as using the much larger-format Magic flavour), be more confusing to drivers, have issues with sight lines, lane paths, the need to drastically vary speed to make it around the tightest parts without holding everyone up on the straighter bits, etc. There's a few of these near where I live, and they're pretty lazy, awful solutions to a problem that shouldn't really have existed in the first place if a few more pounds had been invested. Whereas a few other similar junctions have double roundabouts (or even double really-big-"mini" roundabouts, oddly) and, once you've briefly adjusted to the idea, work just beautifully - more consistant speeds (themselves a factor in smoother flow), less overall conflict, better surety of what lane to be in as it's more likely you'll be allowed to pull across "between" the two islands, etc. 193.63.174.210 (talk) 19:53, 17 November 2008 (UTC)

Nothing aberrant about the double roundabout in the Bristol area. I can think of six straight away and they work just fine. I've never thought about the reason for them, I'll have a look when I go round one next - Adrian Pingstone (talk) 08:35, 23 May 2008 (UTC)

Where would you put a single mini-roundabout in the example shown? If it's in the middle, you get awkward acute angles between streets. —Tamfang (talk) 06:12, 29 August 2008 (UTC)

What is this?

Just wondering, what is the proper name for this intersection?? --Admiral Norton ^(talk) 23:11, 22 August 2008 (UTC)

I'd call it a double roundabout, though the far part of it is unclear at this angle. —Tamfang (talk) 06:01, 29 August 2008 (UTC)

It's two roundabouts connected by a very short stretch of road. They serve together as one intersection in the grid plan of the neighborhood. Admiral Norton ^(talk) 20:17, 4 September 2008 (UTC)

Raindrops

The "raindrop" section is quite obscure. The pictures don't show enough to explain what's going on, and the text doesn't give me a mental image that makes sense. —Tamfang (talk) 06:01, 29 August 2008 (UTC)

AFAIK, it's a roundabout stretched like a peanut or a USB stick. Admiral Norton ^(talk) 20:18, 4 September 2008 (UTC)

Direction of rotation

Article currently reads (under Difference from traffic circles): All vehicles circulate around the central island in the same (counterclockwise) direction.

This is not true in Australia, where circulation is clockwise. I suspect the true situation is that it's clockwise in countries that drive on the left (e.g. Australia, UK), and anticlockwise in those that drive on the right (e.g. USA, France, Germany). Can anyone confirm for some other countries? Andrewa (talk) 16:29, 15 September 2008 (UTC)

You are correct: the portion in parenthesis reflected a RHD bias. The intent is that traffic circles sometimes have bidirectional flow around the central island. --Bossi (talk • gallery • contrib) 01:13, 16 September 2008 (UTC)

Hmmm... But this article is quite explictly not about traffic circles. It's about roundabouts.

More important, what it says appears to be false. It's not bias, any more than it would be bias to say that all countries are monarchies. It's incorrect.

Several other articles already have the correct information, so I think we should just fix it. Andrewa (talk) 02:24, 16 September 2008 (UTC)

Fixed. Actually, the correct information was already implied elsewhere in this same article, in the caption of an image in the following section for example. Andrewa (talk) 15:18, 16 September 2008 (UTC)

Rotary?

I'm sure that this has come up a bunch of times, so I'm not going to just change the article, but at least a few New England states, Massachusetts being one of them, have Rotaries that are equivilent to Roundabouts, not Traffic Circles. That is, traffic already in the circle has the right of way. This article and the disambiguation page for Rotary should be fixed. CSZero (talk) 20:06, 16 October 2008 (UTC)

Additionally, I just found the archives for this article, and that lead me to the Portsmouth (New Hampshire) Traffic Circle. In the archives, there was a discussion about this particular interchange. Someone from Europe shot down the American who pointed out this is a Roundabout by the English definition (why we call it a traffic circle and not a rotary in this case is beyond me). His argument was because it doesn't have "yield lane markings." Well, in America, we don't have such markings, we have signs. And if you go to MSN maps and find the thing on the birds-eye view, you will see that little triangle yield sign saying entering traffic does in fact legally yield to traffic already in the circle. So... my point is that in many New England states, rotary means roundabout, and that the line between traffic circle and rotary and roundabout can get blurred to the point where I think we should merge the articles.

Someone pointed out in the traffic circle article that Massachusetts is actually trying to get rid of many rotaries, and this is one place where maybe a rotary does differ from a roundabout. We don't post many speed limit signs on the things, and some of them are massive "motorway" overpasses. In other words, we operate our rotaries with traffic-in-the-circle-gets-priority rules, but sometimes at speeds closer to 50 MPH than 25 MPH. CSZero (talk) 20:06, 16 October 2008 (UTC)

I'm obsessing and I need to go back to work :-) According to [2] which is an American publication that I found linked to this article, the New England Rotary is not a Modern Roundabout, but it is really not a traffic circle, either. If we don't clear this up by merging all of these into a single article, maybe the best bet is to create a seperate article for Rotary, to mean "Most common in the New England region of the United States, a rotary is primarily a mid 20th century roadway design defined as a circular, one way, often multi-lane roadway, similar to a traffic circle or a roundabout, but with key differences. They are often found as overpasses or underpasses to highways. Usually traffic already in the rotary has the right-of-way as in a modern roundabout and opposite of a traffic circle, although there are exceptions. The difference in design of a rotary versus a roundabout or a traffic circle, is such that rotaries tend to be quite large and there is little deflection around the central circle (meaning traffic coming on or off does so primarily in a straight line, not a curve). These two factors mean that rotary traffic often travels at speeds in excess of 30 miles per hour, leading to confusion and accidents, and the resulting unpopularity, that the modern roundabout does not suffer from. Although this is a traffic engineering definition, many rotaries are called traffic circles or simply circles, such as the Portsmouth Traffic Circle, in naming."

Does anyone oppose adding this article and updating the relevant pages to point to it? (and sorry for writing a novel in the course of a few hours!)

Thanks, CSZero (talk) 20:57, 16 October 2008 (UTC)

Alright, about a week and no comments or complaints, so I was Bold and went ahead and did it. CSZero (talk) 14:52, 22 October 2008 (UTC)

Offset roundabout

Offset roundabout

I just came up with this idea for an offset roundabout today, which would reduce the number and sharpness of turns required to traverse the roundabout. This way, if you're going right, you make a smooth right turn. If you're going straight, you just have to jog left and jog right. Has anything like this been implemented anywhere? It might take up a bit more space overall than a traditional roundabout since the approaching streets might have to be realigned (outside the boundaries of this diagram) to approach the circle as a tangent instead of directly. — Jonathan Kovaciny (talk|contribs) 21:56, 7 November 2008 (UTC)

Yes, very similar to an American Rotary (intersection). Please see: [3] for the example I photographed. CSZero (talk) 01:29, 8 November 2008 (UTC)

The entry curve is vital to the safety of a roundabout. It needs to be the sharpest to properly control traffic speeds. Sometimes a tangent exit is used, but tangent entries cause crashes.--Triskele Jim (talk) 21:51, 9 November 2008 (UTC)

I'm ambivalent ... on one hand the fast entry speed may disguise the fact the roundabout is there and otherwise encourage excessive entry speeds... on the other, the fact that it pipes you right into the outermost tangent of the curve puts you at least risk of doing so whilst being in direct violation of other vehicles (you only collide with those turning down the road to your right, rather than ANYONE going past the point where you lose it and crash over the more usual flanged bit), and if you can't handle the speeds of the exit curve, you probably won't have made it to said exit anyway. It puts me in mind of the dual-carriageway exits on british motorway junctions (particularly the one I take to get to work, where I'm pretty sure they added traffic lights with less-than-optimal phasing not for traffic flow control but simply to minimise exit speeds and prevent accidents, as you can still nudge the limits of grip from a standing red-light start if you push hard), but without the matching entry curve. Or indeed, at least in one direction it would be a lot like the one I just mentioned, as in at least one direction there's a "shortcut" lane to the motorway on-slip that first splits off from the other lanes, continues almost completely straight, then curves sharp left to join the main alignment. It's good fun to try and do it quickly when no-one else is around (as there are few physical barriers to just straddling the main curve of the roundabout in order to smooth off the sharpest turn), but all in all could do with alteration as doesn't do much to allow you a safe speed of entry to this fairly steep uphill bit of road (a slip road rising from a lower road to a motorway that is itself on maybe a 1:20 up grade) in either sense of the word.... i.e. you have to go slow in order to make the turn, then have nothing in reserve to build up a decent merging speed. Attacking it more shallowly from the standing start, or slower entry to the roundabout itself, would probably give you better odds, and be less likely to tempt an accident from entering far too quickly (70mph entry road, meet shortcut lane where you don't have to stop, and a sharp 2-lane turn where hitting it at 50 makes your tyres howl... with a big ol' concrete bridge support and embankment reinforcement waiting to catch anyone who misjudges it) —Preceding unsigned comment added by 193.63.174.210 (talk) 19:43, 17 November 2008 (UTC)

Questionable information in "Capacity" section

Quote: "A particular cause of congestion at a roundabout is when many motorists want to make a turn that effectively crosses oncoming traffic. The two images to the right, which presume right-hand traffic, show how opposing drivers making left turns will get into each other's path twice in a roundabout, but in most countries they will not cross paths at a conventional intersection. While always a potential issue, periods of low traffic density typically result in both drivers making simple adjustments to avoid each other and then going on their way. When traffic density crosses a certain threshold however, adjustments to speed and direction are no longer simple, and may not even be possible without circling the roundabout a second time, or even several times, in order to get a proper opening. And often, impatience overrules any inclination for said driver[s] to do other than "go forward"."

I'm not sure if the author of this has actually used a roundabout or understands how they operate. There's no need to be extra careful or there being more danger when opposing right turns (for LHD, or left for RHD). The very nature of how a typical roundabout works - with either traffic entering the system, or less commonly, already on it yielding to the opposite kind - effectively turns it into a small, circular road where your only actions are to merge in and out safely and with proper regard to priority. It's no longer operating under the same rules as an opposing turn at traffic lights. In fact, even if there wasn't this definition and it was a big ol' free for all, it effectively reverses the way you cross the "oncoming" traffic, forcing you to go past, and then turn "nearside to nearside" after becoming clear of the oncoming vehicle, rather than "offside to offside" where you turn with them still in front of you, and still a potential danger should they decide to head straight-on at the last minute.

Also, just how badly are you getting it wrong (or how insanely densely trafficked yet somehow still fast-moving is it?) when you regularly need to execute two or more complete rotations of the island in order to carry out a simple turn? That shouldn't even be necessary on l'Arc de Triomphe. Somewhere, you have seriously missed the point and the method of approaching these things. I've had to do multiple circles once or twice before - but only because I'd lost my bearings, hadn't seen an approach sign, and was having to do a couple of moderately slow laps to read all the exit signs instead before choosing which direction to head. And once - once only - had to take emergency avoiding action and divert for a second go-around when cut off from my rightful path down the "fast" lane of a 4-lane road (from the middle ring of a 3-ring island) by some complete nobber who thought it perfectly alright to continue round to the next exit in violation of my lane without signals, acknowledgement of screeching tyres/horn/lights, or anything. Typically so long as you are at least partway intelligent about choosing your entry & exit points (e.g. in the above, don't intend on turning right from the left-hand lane on a clockwise rotation), use your mirrors and signals, and have a basic level of wit about you (optionally including that to gracefully recover from making a huge mistake in your intended path), it's a reasonably simple affair, even if it's not one that's guaranteed to be fast.

I really don't like having to write what feels like a flame at someone, particularly as I'm still on an anonymous account, but... damn, driving-noob. Do the research before writing? Yes, a large amount of cross-traffic preventing you getting onto the island in the first place can certainly cause congestion (and I've been stuck in a lot of it both when there's no gaps to be had, and behind people who can't identify the rare, cavernous ones), but the rest of it is wierd. 193.63.174.210 (talk) 19:32, 17 November 2008 (UTC)

"Deflection"?

Maybe this is a UK thing? I don't understand what "deflection" means in this article. It does not appear to be talking about Deflection (engineering), Deflection (physics) nor any other definition of the word I am aware of. 141.151.2.144 (talk) 02:17, 5 March 2009 (UTC)