The Case for More Traffic Roundabouts | Hacker News Reader

The Case for More Traffic Roundabouts

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65 pointsOletros80 comments

It was a revelation when driving through the UK that driving could be enjoyable again. In light to moderate traffic, there was rarely a need to stop. In contrast, in the US, it's stop/go/stop/go. Even in heavy traffic, the roundabouts were better in terms of throughput and safety.

Roundabouts stop being useful once you get to "gridlock" style traffic, though. Because the traffic tends to work its way back into the roundabout and clog the whole thing up. I experienced that this spring in Scotland on a visit.

So long as the traffic flow is at least the double-digits (mph or kph) roundabouts are just fine. Below that though, and there be dragons.

People tend not to jam up intersections with stop signs unless there's a bit of space for them on the other side of the intersection. Same for stoplights, although there are some cases where traffic backs up into the intersection though that generally has more to do with people who are moving (albeit slowly) and then everyone jams on the brakes all at once, stranding several in the intersection.

In Sweden we have a lot of roundabouts (and we also love to brag about having the world's lowest road fatality rate) -- what I see a lot for big roundabouts is traffic lights before entry. Best of both worlds.

With the lights on the roundabout entry points, it flows better than a regular signaled intersection, as left turns are no longer an issue.

That's the question I had. I had a very good experience with roundabouts driving around France for two weeks, but as a resident of Manhattan I wondered how they would fare under extremely congested conditions with many aggressive drivers. (I imagine they have those conditions in Paris -- but in Paris we took the Metro.)

In Paris, the most traffic-heavy roundabout (place de l'Étoile, around the Arc the Triomphe) has different rules from most others, cars on the roundabout must yield to those entering.

I'm not sure it improves safety, but I think it helps preventing gridlock.

My experience in Nantes, a city with a lot of roundabouts (know for double roundabouts[1] and square roundabouts[2]) is that double roundabouts seem a bit better when there is congestion.

Usually when there is congestion on a roundabout, people on the roundabout will let every other waiting entering car pass before them, anyway. I think it works quite well.

[1] https://www.google.fr/maps/place/Rond-Point+de+Rennes,+44300...

[2] https://www.google.fr/maps/place/Place+du+G%C3%A9n%C3%A9ral+...

Ha yes, double roundabouts, never seen them outside Nantes.

It gets fun when you have the tram line going through 1

I live in a city called Al Ain in the UAE. It's quite known for the sheer number of roundabouts. Due to heavy congestion at some of them, they've started replacing them with either intersections or roundabouts with lights.

How does congestion happen? A roundabout typically has four entrances. During peak traffic, one of these entrances might get clogged. This one side causes the other four sides delays due to right of way. Say a buildup forms at another side because of the delay. The other sides will be even more affected. This snowball effect is usually what causes congestion at peak traffic.

Traffic intersections on the other hand are immune to this issue because the delay depends solely on the light's timing, making it way more predictable.

I blame the stop/go/stop/go feeling of US driving more on the grid rather than the lack of roundabouts. 4-way intersections are relatively rare in the UK, most minor road intersections being T-junctions.

City planners are aware that continuous driving is enjoyable and go out of their way to eliminate that enjoyment wherever possible. It's called "traffic calming," though I'd argue the results are the exact opposite of calming.

Drivers who are comfortable, having fun, and moving continuously are much more likely to speed and get in accidents than drivers who are annoyed and constantly vigilant for conditions changing second-to-second (like stop-and-go traffic).

They missed out on the biggest problem with roundabouts: Their worst-case traffic behavior is cancerous. If any single exit is blocked, entry traffic will become blocked in all directions. And if the road grid is dominated by roundabouts, the problem grows in all directions.

It's not a problem when traffic is just congestion. It's hardly a common problem at all. But when it is a problem, such as is the case with a traffic accident that blocks multiple lanes of traffic, it causes full-stop gridlock to grow outward to the point of full paralysis.

The worst traffic jam I have ever been in was not in NYC, Boston, Seattle, or San Francisco, but rather in Idaho Falls, Idaho on a normally empty country road that was running parallel to the road where a drunk driver caused an accident that blocked the roadway. That single accident caused me and hundreds of other cars to sit in the same spot for almost 4 hours.

When traffic density is high you don't build roundabouts. Or if you do you then put part time signalling on them.

But that's just the point. Traffic density should never be high in Idaho Falls. If you can break the grid to the point where people are in gridlock in Idaho Falls, you've done something wrong.

One some larger roundabouts in the UK (and no doubt other European countries), they have traffic lights on the roundabout, between exits (I'm not talking about the entry lights). If one exit is totally blocked, these lights can allow traffic to continue out of other exits.

One more problem is pedestrian crossings. With a traditional intersection, only cars changing direction cross the path of the pedestrian. On a roundabout, when you cross one of the exit arms, your path is constantly crossed by drivers going straight through, doing a right turn, doing a left turn and doing a U-turn. They are all driving at full speed too, rather than just starting from a stop. It is a delicate game where you gently put your foot forward to signal your intent, wait for the incoming traffic to stop for a moment, then dash to the other side. This is generally my experience, but maybe in other places drivers treat pedestrians on zebras differently.

"your path is constantly crossed by drivers going straight through, doing a right turn"

It's only crossed by the same amount of drivers than a regular intersection: those going on the same street as you.

"They are all driving at full speed"

Actually no, the curve of the roundabout (for properly designed roundabouts) slows them down. In fact a traditional intersection causes them to drive even faster since many drivers go in a straight line.

"It is a delicate game"

The nice thing about roundabouts is that you only have to check for cars coming from ONE direction, as opposed to a traditional intersection where cars can come from behind you, from your side, or from in front of you. So crossing a roundabout requires less cognitive bandwidth.

At busier intersections I find traffic signals much nicer as a pedestrian, because while the same number of cars do cross your path, they don't cross your path when you have the walk signal, which is when you'd actually be crossing the intersection. It gives you a nice break in traffic rather than having to push your way out and hope traffic stops for you. This is assuming no right turns on red (as in most of Europe), and left turns only on left-turn signal (typical in cities, at least on major roads). In those cases, there is no traffic at all allowed to enter the crosswalk when you have the walk signal, so you have an exclusive protected crossing.

At lower-traffic intersections the difference is less pronounced, partly because it's easier to force your way across even without a signal, and partly because the signals at less busy intersections may not give pedestrians an exclusive period in the cycle anyway (e.g. by allowing left turns on a regular green).

This might be Copenhagen-specific, but in Copenhagen I also find roundabouts make the pedestrian/bicyclist interaction less clear. At regular intersections, bicyclists can't cross your path when you have a walk signal, but at roundabouts they seem to just go through and are less likely than cars to stop preemptively when they see a pedestrian wanting to cross. Roundabouts aren't very common though, so maybe this would be worked out if there were more of them.

"I find traffic signals much nicer as a pedestrian"

You may find them nicer, but they are not safer. The data already shows roundabouts are safer. As the article reports: "researchers have found that roundabouts reduce [...] pedestrian/cyclist incidents by 40%"

That study was specifically in the USA, whose signalized intersections are not really pedestrian-friendly to begin with. For example right-on-red is permitted almost everywhere (except NYC). In that context, I could believe that roundabouts are less bad. I would be interested to see how the comparison generalizes, for example a study of roundabout vs. signalized intersections in Denmark or Germany. It's still of course possible my feeling of more safety at signalized intersections in Denmark is wrong.

Sweden takes an interesting approach in combining both. There are a lot of roundabouts, but most of them also have a signal at the entrance. This makes it easy to cross as a pedestrian, because your crosswalk at the roundabout entrance is protected with an exclusive signal cycle. That forces a gap in traffic instead of you having to force the gap by trying to step out. Possibly even safer than either option alone?

I don't have a study at hand, but in Germany, too, it is generally accepted that roundabouts are safer.

You're wrong about pedestrians. The crossings are upstream of the roundabout and you only have to deal with two directions of traffic.

Not the one I have to cross. The crossings are right where the exit/entry roads begin/end. Which makes sense, since that's the natural progression of the sidewalk and there are two bus stops on the roundabout, so people have to cross right there to reach them. A picture is usually worth a thousand words: https://www.google.com/maps/@42.6686834,23.366936,3a,75y,165...

> If any single exit is blocked, entry traffic will become blocked in all directions Typically in the UK, if the traffic is this bad, then drivers on the roundabout leave gaps to enable cars going in uncongested directions to get through.

This "biggest problem" also occurs with traditional intersections.

In both cases, traditional or roundabout, drivers are supposed to leave gaps in the traffic to at least let some cars through the intersection.

In both cases, if drivers don't follow that rule gridlock will ensue. In fact, 2-3 cars stuck in the middle of a traditional intersection is often all you need to completely block entry and exit traffic by preventing anyone from going straight or making left turns: https://en.wikipedia.org/wiki/Gridlock

In New York City the rule is "Don't block the box" and it carries stiff penalties.

I always found it funny how easy it would be to DDOS a roundabout. Get 10 friends together and drive around in a circle all day.

Couldn't you block any intersection pretty easily with 10 cars dedicated to doing so?

But then you would be clearly breaking the law, unlike someone just driving around and around

That actually happens: cyclists have found that to be a very effective and infuriating way of protest on several occasions. You can find lots of Youtube videos.

Denver has a handful of growing roundabouts in newer neighborhoods, but unfortunately they keep installing them in all the wrong places. I'm convinced they are "testing the waters" by placing them in residential neighborhoods with very little traffic, which honestly just makes people annoyed by them, rather then appreciate them.

Roundabouts aren't a replacement for stop signs, they are a replacement for stop lights.

I remember when they installed one out in Littleton (suburban Denver) - it flows traffic spectacularly but it took years, maybe even a decade for people to get used to it.

I once came upon it and found a full size four door sedan in the (raised) island in the middle with four befuddled teenagers standing around shaking their heads. They had plowed into the traffic circle straight ahead, jumped the raised embankment and landed right in the center island.

But the roundabout saved them. If they were not paying attention, as clearly they weren't, then they could have had a collision in the centre of an intersection. Better to end up in the he Center than t-boning a car.

Some of the most egregious roundabouts I've ran (heh) into have been in Aspen. They're right after you get off 70 (ie going 65/70 mph) and are often overgrown with bushes and trees. I'm all for roundabouts, I think when done right they're great, but I don't know what they were thinking when putting these in.

https://www.google.com/maps/@39.6439352,-106.3776606,248m/da... (2008 footage) https://www.google.com/maps/@39.6277372,-106.4200775,185m/da...

That's actually Vail, not Aspen.

Yeah, you're right. I had the maps right, but name wrong.

They just installed a pair on the new Pecos bridge over 70. Those are really nice uses of roundabouts, so maybe we're starting to "get it"?

Yes, I was going to mention the only one that really works well is that pecos roundabout since it's actually solving a real traffic problem.

Light traffic residential areas are a perfect place for them. There's nothing more annoying than observing a stop sign in an empty road. I have roundabout near me and when there is no traffic on the roundabout you just drive through it. The residential roundabouts have only a slightly raised centre so you can drive through in almost a straight line.

Late at night when there is no traffic it saves having to stop at all.

I wonder if it would be cheaper to install "Rolling Stop" signs.

I think the exact opposite, that four-way stops should for the most part become roundabouts, and that's it. And actually, just four-way stops between two-lane roads, once you start adding lanes it gets too complicated.

In Spain, basically everything is a roundabout, so much so that when the roads are big enough they have lights within the roundabout. That's way too much IMO.

I live in Victoria, Australia, and we’ve had roundabouts for ages. I think they are very good for a certain scale of road/traffic. Mostly intersections with moderate amounts of traffic on average, and not high-speed. e.g., the main intersections within housing estates. Having too many of them instead of give-way signs drive you a little batty (I’m looking at you, Warrnambool) while really heavy traffic, major intersections work better with traffic lights.

My daughter recently got her learner license, and she has found roundabouts one of the trickier intersections to navigate. You have to read the traffic flow. This person about to enter on your right is going straight ahead, so will block you entering the roundabout[1], but they have to wait for that person coming the other way from you and going straight through, so you can slip in the gap that creates without cutting anyone else off. As with many things it is familiarity and practice that makes them work[2]. I think roundabouts work very well here for the most part, and my daughter is getting pretty good at reading the traffic. It’s not rocket science[3].

The science of roads and traffic I imagine is a surprisingly nuanced expertise involving a lot of physics and psychology. I find when I cross over the border to New South Wales I feel like a long-tailed cat in a room full of rocking chairs. I eventually figured out it was because the signage was a different distance before the intersection compared to my home state. Once I was aware I could adapt.

[1] We drive on the left side of the road because Australia is in the southern hemisphere.

[2] I bet the first traffic lights caused an uproar. “Why the hell should I stop just because there’s a red light?!”

[3] Oh wait, actually, it is rocket science.

> Having too many of them instead of give-way signs drive you a little batty (I’m looking at you, Warrnambool)

My parents just moved to Warrnambool from Mildura. One of their first comments was on the lack of roundabouts :)

You can't discuss roundabouts without a mention of the magic roundabout in Swindon, UK. A big roundabout made up of 5 small roundabouts. https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)

I encountered it once and don't ever intend to do so again.

I grew up in Australia in a town nicknamed "The city of roundabouts", I know a thing or two about them.

Upon moving to North America, it was shocking to encounter my first 4 way stop. To this day I still shake my head every time I encounter one. They are non-existent in Australia.

It's been amusing watching the resistance of North Americas to roundabouts, I think, because they are never taught how to use them. Sometimes I ask people the correct way to signal in a roundabout, and I swear I've never had two people in the same room agree.

The city of Calgary installed one, and it was taken out soon after because of a public outcry. In another city in North America I lived in, they put one in, and a lady promptly drove straight through it, crashing her car. She sued the city and one, because it wasn't fair to go and put in a roundabout like that.

There's a bunch of roundabouts in Calgary, though admittedly they're not common.

One of the odd things about moving from Italy (where they've had them for a while) to Bend, Oregon is that there are actually a ton of roundabouts here in Bend, for whatever odd reason. People seem to handle them just fine.

There are two problems with roundabouts in America.

The first problem is the people who don't know how to drive. I cannot count the number of times I have seen people stop in the middle of a roundabout to let cars in, or stop at the entrance and stare in confusion when there is absolutely nothing coming.

The second problems is inherent in the design. A line of traffic that is going straight can, effectively, prevent any cross traffic from entering the roundabout, due to the small radius of most US traffic circles. This is a trade-off, of course, and is still safer than traffic lights or a 4-way stop, and usually more efficient.

The first problem is a problem with US drivers in general. I don't know what we should do about it, except perhaps test people's driving abilities more frequently. I, for one, honk at people who fuck up my roundabout experience.

I think the second problem is an acceptable tradeoff, but ymmv

I see the first problem all the time, especially at stoplights. Often when there is a line of cars waiting at a red light, when it turns green someone will remain stopped so that a waiting vehicle on a perpendicular street or nearby business can pull onto the highway in front of them.

They think they're being polite, but they're forcing dozens of cars to wait for an additional cycle of the stoplight, whereas if they had just pulled through the light as normal then the waiting car would get a chance to merge as traffic either cleared or came to a stop again.

"dozens" is quite a bit of hyperbole. I generally only see behavior like this when traffic is dense and the speed of traffic is limited. In those cases, letting someone in doesn't decrease the number of cars that make it through the light. Additionally in those cases, it's quite possible that if nobody lets in the the car trying to merge, they will never be able to merge.

Obviously, optimal behavior is dependent of the traffic conditions.

"Dozens" is not hyperbole at all, my account is an accurate and truthful statement of the traffic conditions in my area and the consequences of those bad actors.

Cars looking to merge should do so as the traffic comes to a stop. A car already on the highway they are looking to merge onto need only stop sooner than they otherwise would, allowing them to pull out into traffic that is already at a standstill.

I see this too, in the bay area. There are so many intersections with green left-turn arrows that drivers forget the rules when they encounter a regular light without a left-turn arrow.

The particular case is that a driver going straight will yield to a driver approaching from the other direction who wants to turn left across them. They should not yield. They have a green light.

I'm not sure I understand the traffic conditions you are describing.

Lets take "dozens" to mean "atleast 18" (a dozen and a half). The average car is 15ft so this means to fit the 18 cars bumper to bumper there will need to be at least 270ft between the car you let in and the car in front of it when it passes out of the intersection.

If you leave half a car length between cars and allow the full 2 dozen this number quickly becomes 528ft.

If people are really this slow in pulling out, I feel your pain. However it is these numbers that caused me to judge your anecdote as hyperbole

Additionally, you suggested blanket solution sounds more dangerous as well as completely unworkable in bumper to bumper trafic: "Cars looking to merge should do so as the traffic comes to a stop."

It's far more dangerous to pull out in-front of a moving and already braking car that may or may not see you then to pull out in-front of a stopped car that has indicated that it does.

It seems that the slight inefficiencies you cite in the first complaint would eliminate the phenomenon described in the second complaint.

The point of roads is not to transport any particular traveler at the greatest possible speed, but rather to transport all of us in safe and convenient fashion.

Interesting observations. As a counterpoint, there are a couple of roundabouts between here (Phoenix) and Las Vegas, notable both because there's often fairly heavy traffic and that almost everyone on the road is from elsewhere (and therefore unfamiliar). They seem to operate quite smoothly, and are a welcome break from waiting for several cycles of traffic lights.

I'm curious... where have you seen these troubles? Perhaps the small radius is the real issue?

There are a couple of roundabouts where I live, and I see the second problem all the time. The best (worst?) was someone who came to the entrance, stopped, sat there for about 3 seconds and then went when there was a car coming in the roundabout and nearly caused a collision.

Simple educations campaigns would solve the driver education issue. Get all networks to run ads with celebrities showing how to drive in a roundabout. You could throw in some non-texting message while at it.

The ignorance argument is difficult to agree with because every country has had to introduce them to an uneducated population at some point. You could have used the same argument against traffic lights.

The most straightforward designs of roundabouts don't have a good safety record for cyclists. This post gives some hints based on the Dutch experience http://www.aviewfromthecyclepath.com/2014/05/the-best-rounda...

Roundabouts are unfair. They don't balance traffic loads symmetrically.

Here is what I have observed at one near my house: as you approach the yield line, you can't enter the circle if someone has just entered it on your left. So, if you have lots of cars approaching northbound, and lots of cars approaching westbound, the northbound cars will be on the left of the westbound ones, and will block their entry. You end up with a huge queue on the westbound lane.

This is exactly what happens every day at the evening rush hour (and of course the southbounders block the eastbounders in the morning).

A traffic light would be much better, because its red/green intervals can be tuned to observed traffic tendencies for the time of day.

There's two types of round-abouts: the Continental European kind and the UK/Australian kind. The UK/Australian kind are designed to keep traffic moving, so the angles are arranged to make entering similar to a merge. European ones are designed to slow traffic, so you enter at a right angle and have to turn hard to enter.

The UK/Australian kind kill cyclists[1]. I understand the European kind are safer, but I don't have personal experience with them (OTOH, I have been hit at a roundabout, and seen another 2 car/cyclist accidents).

[1] http://acrs.org.au/files/arsrpe/Cumming%20-%20High%20rate%20...

[2] http://search.informit.com.au/documentSummary;dn=38012654206...

Roundabouts don't kill cyclists, unobservant drivers kill cyclists. They kill cyclists on the straight and at intersections too. Don't blame the roundabout for it.

That's correct of course. However, roundabouts increase the risk enormously. I assume you read the stats in my links?

49% of crashes at roundabouts involved cyclists

It specifically addresses the "look but didn't see" problem, and how the Australian design makes that worse: Herslund & Jørgensen videoed cars and cyclists at roundabouts and noted that bicycles are often located in drivers’ peripheral vision. They suggest that experienced drivers use fast search strategies such as concentrating on where cars usually are, so may be more prone to LBFTS collisions than less experienced drivers.

Roundabouts are great, dependent on traffic flow. If you have large amounts of traffic moving in one direction, it will prevent traffic flow from the direction that has to give way to it. In New Zealand, we use a lot of roundabouts, but often congestion easing requires replacing roundabouts with traffic lights to merge two incompatible streams of traffic.

I live in upstate NY, where the DOT is very passionate about installing roundabouts everywhere there is development, as they optimize use of undersized roads, especially in sprawly suburbs. (Search for "Malta, NY" on Google maps and check out the 6 consecutive roundabouts around the I-87 exit)

The problem is they are a cyclist/pedestrian death machine, and the bigger ones cause lots of small accidents. Looking out my office window, I've personally seem a strategically placed streetlight get plowed over about 8 times due to some of the engineering defects of this particular roundabout.

The roundabout in China pictured in the article included an elevated pedestrian walkway -- a feature nearly completely absent in US implementations.

The case of France is a quite simple. Governement wanted to lessen road related death, so they actually subventionned city and state to build roundabouts.

They are flourishing everywhere, but at this point there is not much need for it anymore. But they keep building them to keep their subventions, it redistribute money to local company (and also keep mayor in their place).

Sometimes you can drive 100Km without encoutering a single crossroad but hundred of useless roundabouts, it actually reduce speed on main road and provide little but no value to actual cross section.

Half* of the UK's roundabouts are in Skelmersdale, and they provide little function because there are so few cars on the road in the area. They probably increase emissions because you've got to drive that much further to get where you want (The largest of these roundabouts is half a mile in circumference) - and with nothing but grass, woodland and strange "art" sculptures in the middle, they're a huge waste of land.

*Approximation

The most curious definition of 'waste of land' I've encountered in a while. Are national parks also a waste? How about wildlife refuges? Oh! Scotland! That may also qualify.

National parks are places of outstanding beauty. I can assure you Skelmersdale is not.

By waste of land, I mean the place was built using several times more land than was needed for the relatively low population, but some clever fool with government money decide they'd build a bunch of small ghettos separated by large roundabouts.

Sounds miserable. I was imagining a bucolic wonderland of natural beauty, with birds nesting and ancient oaks over shady glens.

My local town is in the process of sticking 'roundabouts' everywhere. Mayor visited someplace and liked them; he's pushing them on us now. Sometimes its just a dumb island in the middle of an intersection; you have to crank around it at microscopic speed which benefits no one.

The worst one has two lanes halfway around; one lane the rest of the way. From the south you can take the right lane and exit north without turning (much). But nobody understands the point; everybody stops and creeps around. So they put up a map(!) so you can figure it out. And 13 arrows and warning signs. All in the interest of 'efficiency'

If they replace a stop sign, then they're strictly better in terms of fuel economy, right?

A large problem with roundabouts is that municipalities tend to build them as poorly or put them places where a light should be.

>filling the center with landscaping that obstructs view

>putting them where a computer controlled light should be (small road meeting large road, stays green toward large road the vast majority of the time)

>put them where a flashing yellow/red should be (tiny road crossing main road

>putting roundabouts in areas that see a large volume of heavy trucks

Roundabouts don't work very well on roads with highly differing traffic volumes

I love roudabouts. I've seen the great use of them the very first time I've used them. I've always thought of traffic patterns as being the largest time suck of our modern lives. Two solutions to this. Install roundabouts or take over the stop light manufacturing and production in America with a startup. Sadly neither have happened due to the large need of capital to make either happen.

I hear the argument "Americans don't understand roundabouts, therefore we wont build any" quite often in these kinds of articles. If you survey people about something they've never comes across before, of course you're going to get negative results.

If Americans can drive and talk on their cell phones, they can handle a roundabout.

There are plenty of them in Maryland. They work great.

Somebody gave me the argument in NASA that the US didn't switch metric because the cost would be too high because they are so big. Ireland and UK have gone metric in our lifetimes.

I mean, there are lazy people throwing out platitudes to justify doing nothing wherever you go.

If you asked farmers what they wanted in 1900, they would have said they wanted a horse that ate half as much and did twice as much work.

What they ended up with was a tractor.

More, but only those little ones where the island is smaller than the road so that motorcycles can fly strait through.

Small roundabouts do not work. Here in San Francisco the small ones (out in the burbs) jam up with few cars and are littered with minor car debris.

Obviously it will vary, but my experience in the suburbs of Minneapolis/St Paul (and driving in Europe and Australasia) has been the total opposite. Instead of stop sign hell every block causing gridlock during busy times traffic actually flows. "Minor car debris" likely comes from drivers who don't understand driving etiquette (use your bloody turn signal!) rather than road design.

The mini-roundabout's success suggests otherwise: https://en.wikipedia.org/wiki/Roundabout#Mini-roundabouts

The Case Against Traffic Roundabouts.

https://www.youtube.com/watch?v=iAgX6qlJEMc

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