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propter_hoc

My best friend is a highly experienced civil engineer, specialized in designing intersections. His take on roundabouts:

- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle

- They reduce T-bone collisions

However:

- Small fender benders and sideswipes are much more frequent

- They use way more area

- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).

- Finally, they're also (mostly) worse for cyclists and pedestrians.

Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.

View on HN

I live in the UK, which has roundabouts, mini roundabouts, double and triple roundabouts, traffic-light controlled roundabouts, and magic roundabouts. They work perfectly fine.

The difference is that traffic flows very differently in the UK to the US. In fact, the way traffic flows in those two countries captures a lot of their cultural differences. In the US, everything needs a grand overarching theory and imposed order, which is why Americans need traffic lights, and why they’re so keen on a very specific set of liberties that allow them to freely live such similar lifestyles. The UK embraces mild chaos and ruthless pragmatism, with everyone finding locally optimal solutions to their own problems, so things like roundabouts fit well with the national mindset.

I agree with this, and I'll offer a rationale.

Because the US largely "grew up with cars", the economy was built around the expectation that folks can drive to work. The population density of the US reflects this, and mass transit just doesn't work in small/middle America. That means everyone needs to be able to drive. If you can't drive, you can't work. That isn't the case in the UK, and you'll notice a lot of these "driver beware" analysis is explained by the fact that driving in the UK is seen as a privilege whereas it is a right in the US. This sort of "mild chaos" is prohibitive for a lot of would-be UK drivers, and they just take the bus.

The UK has an over-reliance on roundabouts for junctions with motorways and large roads. They are also missing out on Turbo roundabouts, which are super cool and very common in the Netherlands.

The UK’s spiral roundabouts are the same as Dutch turbo roundabouts.

>They work perfectly fine.

I don't want to celebrate UK roads too much. The majority of roundabout users in the UK are not indicating properly. Too many people are stopping at them when they have priority. Lanes are just a suggestion and using the correct lane is an invitation for someone to drive into the left of you.

In other areas: enough people don't know how to use a slip road that it becomes a problem to those who do. Likewise the flashing ambers of a pelican crossing. Lane discipline is much worse than on the continent, to the point you can see it creating traffic jams. Lots of people are driving big cars without the confidence needed to remain in their own lane.

There are millions of drivers who've never passed a theory test. We could do with more ruthlessness.

I feel like you're singling out UK drivers without much evidence here, I've driven lots across continental Europe, although mostly Spain<>France<>Germany<>Nordics, but in all countries people tend to not indicate properly, inside of roundabouts or outside of them. I'll admit to people in the Nordics being slightly better at signaling, but they make up by being so scared and non-confident in their driving that their hesitation causes near-accidents, rather than the opposite.

Still, all across the world the average driver seems to below what I imagined the average driver to be, before I started driving myself.

All of that is user error. The roads themselves might be in disrepair, but are otherwise well-designed.

It may be user error, but that doesn't mean roundabouts aren't a footgun. It only takes one driver who doesn't do everything correctly to cause problems. It's not much fun driving around in the correct lane, only for someone to pull alongside you to the left (equivalent of "right" in the US, of course!). I failed a driving test because someone cut across me on a roundabout.

"I failed a driving test because someone cut across me on a roundabout." That driver may have cut across you on that roundabout but that doesn't mean roundabouts are a footgun.

If a given tool tends to have a high amount of user error, odds are there's a problem with the tool

I mean, what you're trying to minimise is (frequency of misuse x consequences of misuse). signalised intersections target the frequency element, roundabouts target the consequences.

When comparing two interfaces and one allows a larger amount of user error that interface is inferior.

The point is roundabouts require more work to navigate correctly than a four way intersection with traffic lights. Thus drivers are more likely to navigate incorrectly.

> When comparing two interfaces and one allows a larger amount of user error that interface is inferior.

Seeing a safety issue and ignoring all other considerations is an excellent example of the ‘overarching theory and imposed order’ I argued that Britain rejects in my first comment.

I’d rather have more small non-injury accidents if it means fewer injury accidents

Yes, we're discussing how the users change the way traffic flows.

Not gonna lie, I know about the flashing ambers of the pelican crossing, but they are uncommon enough, whenever I see one, I spend several seconds wondering what is happening, until it clicks it's one of these crossings.

Try Spanish roundabouts. On the whole, poorly designed, implemented and regulated. On roundabouts with two or more lanes, laws favour those on the outside lane, so everyone takes the outside lane even if they are travelling 3/4 of the way round. As a result drivers who are in a position to take an exit, do not take that exit. In addition, indicators are not used by most drivers, or they simply leave their indicators on all the way round. In addition, it is not allowed to exit a roundabout from the inside lane even on to a two lane exit. In addition many roundabouts have three lanes to enter onto a two lane roundabout, or two into one, etc. No one knows the rules, or follows them, and no one seems to care, from the civil engineers right down to the end users. The only winners are repair shops.

In comparison, UK roundabouts are civilised examples of harmonious intellectual etiquette. Enjoy them.

[source] I learned to drive in Swindon, home of the Magic Roundabout.

If you complain about Spain, then go live and drive in Italy :)

Home of the double red light, “you really have to stop”

I live in the UK, drive occasionally in Spain due to Spanish in-laws, and agree wholeheartedly. I didn't know about the "outside lane has priority" rule though. I'd noticed it happening, but just thought it was a national quirk rather than gaming the system.

American, in an area getting more roundabouts. The two most heartfelt criticisms of roundabouts I've heard are:

- I have to pay attention every time I go through one. (Vs. having your mind elsewhere works fine with traffic lights? That might explain some of those T-bone crashes.)

- Certain multi-roundabout intersections are "because the Road Dept. hates us" horrors to drive through. Most-often cited - https://www.google.com/maps/@42.5058488,-83.758072,18z?entry...

From my PoV, roundabouts are generally a good thing. Mostly because local engineering standards for traffic lights are wretchedly low - so I can get where I'm going far faster through roundabouts.

As a European, that roundabout intersection looks fine? It might be slightly annoying to have to use all three roundabouts if you're exiting the highway northbound and want to take the southbound local road, but with the amount of exits there I can't imagine a junction would be better.

To an American it looks painfully small and slow for coming off a highway and would be overwhelmed often with cars and semi-truck traffic. One semi-truck would stop an entire circles worth of cars with its ass end swinging in and out. And highway travellers are going to be gun shy and not respond as quickly to gaps in the circle after doing 75+mph for an hour or more.

"They work perfectly fine."

The fact that you mention light-controlled roundabouts highlights that they do not, actually, "work perfectly fine".

Roundabouts are a practical example of the tyranny of the majority; minor traffic flows suffer against major. The centre of Salisbury is a perfect example, constantly gridlocked at two roundabouts except at odd hours on a Sunday.

Adding traffic lights to 'fix' this problem then leads to tailbacks on the major routes and congestion on the roundabout, such that the timing sequence for the minor routes are subsequently reduced, returning to the original problem.

Roundabouts, in the plurality, are used as a lazy 'solution' to at-grade traffic crossing, which the road designers themselves presumably don't have to suffer. They also cause pollution from brake dust from slowing and exhaust fumes from accelerating.

> The fact that you mention light-controlled roundabouts highlights that they do not, actually, "work perfectly fine".

I don't think anyone is claiming that roundabouts work in every and all situations: design handbooks often say they're good 'up to X vehicles per hour/day'.[1] But that does not mean they do not work, or not useful, for <X.

Intersections are an engineering problem, and there is a hardly ever an engineering solution that works everywhere and always. There is usually a spectrum of solutions for the various situations that are faced.

[1] https://www.fhwa.dot.gov/publications/research/safety/00067/... § 1.6.1, 3.3.1

Well we have very different experiences driving to, through, and around Salisbury. There's traffic, and it can get bad, but it isn't as bad as you say.

The council and national highways are working on it, but the problem is not one of roundabouts - its one of increases in traffic and lack of capability to make the roads bigger and/or build a bypass. Unless we're willing to knock down a load of housing and cultural sites we're stuck with something around or slightly more than the road capacity we have.

I have no idea what this means but I love it!

In very heavy traffic conditions I suspect that roundabouts can gridlock all directions in a worse way than a standard intersection with a yellow box because everyone tries to enter the roundabout then they get stuck in it, and then the whole traffic is brought to a halt, including directions that should be unaffected. This happens very often where I live.

> the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery.

Slowing/calming traffic like this is a good thing. Make it impossible to speed. Enforce the existing 35mph speed limit via concrete rather than allowing cars to rip through a yellow light at 70mph. You're also ignoring this aspect when you call roundabouts "(mostly) worse for cyclists and pedestrians".

A place where traffic slows down, without actually stopping, and becomes congested with no time/space gaps between vehicles, is worse for pedestrians.

No it isn't unless all driver all break the law and don't stop for waiting pedestrians.

That's a thing that happens.

But then, how come you blame this on the existence of roundabouts and not on the lawlessness of drivers?

Because driver compliance with red traffic lights is far, far higher than compliance with pedestrian right-of-way rules.

And the reason is obvious: when the driver runs the law of the red light, they run into a law of physics (cross traffic).

The traffic has to yield to pedestrians when entering and exiting a roundabout, period.

Not in UK.

However there are often pedestrian crossings across the roads or the volume is low enough pedestrians can easily cross. A local roundabout got busy enough we had crossing added less than 10 years ago and the biggest road there was a minor B road.

I am a pedestrian due to sight issues and have found very few places where it is difficult to cross when needed.

The "when needed" suggests that there are plenty of difficulty to cross intersections, you're just able to avoid them. Is that accurate?

No it just means I can't remeber any at the moment – but I am, dure some can be found.

This is true if you can alter the properties of the physically existent universe, else it is not true, and, indeed, drivers do not even slow down largely because they feel frustrated when traveling along a road with a 45 MPH speed limit at an average speed of 20 MPH.

> becomes congested with no time/space gaps between vehicles, is worse for pedestrians

Why? This feels like it's assuming pedestrians share the street with vehicles, but besides the US and some other places, don't most "modern" countries have separate pavements/streets for pedestrians? Besides in the country-side, vehicles and pedestrians don't generally share the road in populated areas here in Spain. For crossing roads outside cities, building a pedestrian tunnel below or a bridge above seems to preferred here, except in the cases where it isn't possible, and in cities obviously.

In my city in Norway, at least, there is never a traffic pattern where it's not either:

* a small roundabout with really clear pedestrian right of way marked

* a pedestrian path that takes you over or under the road instead of crossing it

It's great!

[flagged]

Right, you're talking about "traffic participant", are you including pedestrians or not? Because as I said, in many places, "vehicles" and "pedestrians" are well-separated and don't impact/affect each other, so not sure what cluster-fuck could be created there. Seems less of a cluster-fuck than relying on cross-walks and stop-lights?

[flagged]

Posting like this will get you banned here. If you'd please review the site rules and stick to them, we'd appreciate it:

https://news.ycombinator.com/newsguidelines.html

There used to be an epidemic of cars striking and killing pedestrians. The advertising industry (hired by the auto industry) came up with the new imaginary crime called "jaywalking". This diverted attention from the killers and onto the victims. Just one more version of the victim blaming that derives from the Just World Hypothesis.

https://en.wikipedia.org/wiki/Just-world_fallacy

> […] is worse for pedestrians.

Some data seems to conflict with this:

> A 1993 study in the Netherlands examined collision experience at 181 intersections converted to roundabouts. Pedestrian collisions (all injury severities) dropped 73% and pedestrian casualties dropped 89%.

> Evaluations in Sweden concluded that single-lane roundabouts are very safe for pedestrians, at about a 78% reduction in injuries, and that multi-lane roundabouts are about as safe as other intersections.

> A 2002 study of collision experience at the roundabouts in Park City, Vail, West Vail and Avon, Colorado, showed 2 pedestrian crashes prior to the roundabouts operating with over 164 million vehicle movements, compared to 1 pedestrian crash with roundabouts experiencing over 282 million vehicle movements.

* https://www.tac-atc.ca/wp-content/uploads/weber.pdf

> With the installation of a roundabout, this study finds that the before-after analysis results in a 40% decrease in all severity injury crashes for all roadway users, a 70% decrease in fatal and serious injury crashes for bikes and pedestrians, and a 15% decrease in total pedestrian bike and pedestrian crashes.

* https://mdl.mndot.gov/items/202336

OK, so "worse for pedestrians" boils down to a statistic about body hits. If you are not struck, you are not having a worse pedestrian experience. My bad!

It can be a good thing. But I've seen many roundabouts in the US (specifically in the state of Wisconsin) where someone decided to put a roundabout on a major rural highway that was crossed by a side road. In that case there is no sense in having the 60mph traffic stop just for an occasional car crossing or turning. The side road should have a stop sign while the main road flows unimpeded.

The new roundabout completely prevents fatality t-bone crashes into people turning left from those stop signs, which has likely happened multiple times at that very intersection thus prompting the road to be redesigned.

> Small fender benders and sideswipes are much more frequent

Do you have any data on this? Everything I've ever read about them points to exactly the opposite conclusion. They actually reduce accidents and by a significant margin.

My only guess would be that you are referring to the US, where people are not used to roundabouts and yielding without a STOP sign.

Everything I’ve seen says minor collisions (without injury) go up and injury accidents go down.

A good trade

I think that's overly negative. Roundabouts have their place, mostly for low traffic intersections, but I agree that they tend to be overused, also here in Europe. Two examples where roundabouts are not the right solution:

- when there is too much traffic: if there is a constant stream of cars in the roundabout so you have to wait for a long time before being able to enter it, or force your way in (risking a fender bender), that's

- when you actually want traffic to flow. My small city has built a bypass road which is however IMHO completely botched: it starts with a roundabout, and the first exit leads to the route going through the center, only the second one goes to the bypass, so people are more likely to drive through the town. And it has three more roundabouts along the route, further making the option unattractive (in addition to a relatively low speed limit of 60 km/h and several tight curves).

> - when there is too much traffic: if there is a constant stream of cars in the roundabout so you have to wait for a long time before being able to enter it, or force your way in (risking a fender bender), that's

I think it's fine with lots of traffic in a roundabout, but it has to be somewhat balanced.

For example, we have a roundabout that sits on a relatively popular road, with one exit/entry that leads to a bigger highway. During rush hour, there is heavy traffic, from from/to every one of the three points, so traffic naturally divides, as cars turn off.

However, when there is no rush hour, the highway exit/entry isn't used, so cars mostly just pass through the roundabout, and everything still works, as the two entries/exits are still balanced.

Issues would arise if it's only one entry/exit being used, as then it'd always block the two other entries from being used properly, but seems that never happens, so seems to me it's proper and works well, regardless of the traffic being heavy.

Depends on the driving culture and familiarity with roundabouts for sure. Moved from the US to a city in Norway with almost exclusively roundabouts, and it's _so much nicer_. Even in the edge cases, I have never once found myself wanting a traffic light.

Simple intersections can have very small roundabouts, and bigger ones you can connect roads from so many weird directions and have traffic flow well that I would never want to return some of the intersections I experienced in the US.

There are more positives. - They keep traffic flowing better so you won't get "platoons" of cars all moving and stopping at the same time. This is especially effective when you do this in a sequence of intersections. - They calm do down traffic by forcing cars to slow down. - You don't need to install and maintain traffic lights.

Platoons of cars with space in between allow for pedestrians and vehicles to cross the road, downstream.

Nothing worse to have upstream of where you are trying to enter a road, or cross it, than a busy four way stop, with cars coming out of it at regular intervals, without sufficient time/space in between.

As a bicyclist and pedestrian (in Denmark) what is it that’s worse about roundabouts for me? I think they work really well.

I think to an American, a roundabout is this thing that only works for cars and don't take pedestrians or bicyclists into account, with no paths or crosswalks or anything, so hence "Worse for pedestrians". I don't blame them, both roundabouts and care for pedestrians seems uncommon over there, so of course their experience will point towards roundabouts being worse overall.

(UK experience) If you're trying to cross the road leading onto one, it's much harder to tell if a vehicle is going to hit you at speed. I often observe people turning quickly, without indicating, and had I chosen to cross at that time, there would have been some kind of accident. Junctions tend to not have this problem since cars turning out of them are usually going much slower.

I will say 2 lanes roundabouts as a cyclist are a little intimidating when you need to take the inside lane. Drivers are not looking for cyclists the way they look for cars or will rush to get ahead of you or just try to bully you out of the way by entering the roundabout across you illegally and daring you to take the right of way. At particularly busy examples I will dismount and take the pedestrian crossing.

Junctions have their own problems though: Usually drivers will not permit a cyclist to merge in front of them while traffic is not stopped, which means if the stream of traffic is continuous you need to plan your lane change when traffic is stopped by lights.

As a pedestrian, roundabouts with islands (aka all roundabouts here) are vastly superior.

> In those cases, the bulk of traffic all needs to slow down, downshift, …

You know that's like, the entire point of roundabouts: force traffic to slow down.

> They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).

I'm not convinced of this either. It may make sense when considering one intersection in isolation, but over a corridor with ten intersections, you are going to get caught in a red light at least once, and that one full stop will cost you more than all the gains you get from not having to slow 10 mph through each intersection.

This is setting aside fuel efficiency and safety considerations which also favor roundabouts, IMO.

> Small fender benders and sideswipes are much more frequent

But collisions overall are down, and severe crashes down 80%:

* https://tirf.ca/blog/fact-vs-fiction-roundabouts/

> They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic.

While it would slightly defeat the purpose in some ways, roundabouts with traffic lights are a thing:

* https://www.traindrivinginstructor.co.uk/roundabouts-with-tr...

So if one way has heavier traffic (at times), things could be signalized to allow (e.g.) that one direction primarily some of the time and the other three directions the rest.

> Finally, they're also (mostly) worse for cyclists and pedestrians.

Some data seems to conflict with this:

* https://www.tac-atc.ca/wp-content/uploads/weber.pdf

* https://mdl.mndot.gov/items/202336

It would be interesting to know your (friend's) country of origin.

Another pro: they can easily support more than 4 connections

another con: If only one of the exits gets backed up, it clogs the traffic circle and causes every connecting road to back up.

As someone who drives manual, and so actually having to downshift myself when necessary, I would rather negotiate a larger roundabout 100% of the time than having to stop at a red light 30% of the time.

On my current gearbox, I can dip to around 30 km/h and gently accelerate while staying in 4th gear, which I'd be in up to around 50 km/h. So if I hit an uncontended larger roundabout that takes me 50-30-50, I don't have to do anything, transmission-wise.

Manual driving culture is probably one reason roundabouts have been popular in Europe long before North America started to warm up to them.

I don't understand the argument? Seems like you're saying that not having to handle a gear change makes roundabouts better, but that applies to both your manual technique and automatic, so I don't see how Europe would be different from NA?

Also, I'm not a particularly frequent/experienced driver but 4th gear at 30kmh on a roundabout doesn't seem very safe, it does not leave you much control to react to something unexpected (some car coming up that you didn't see, a car who changed their mind last minute about exiting, a car changing lane poorly...). Being able to decelerate or accelerate quickly is pretty important on a roundabout. Not such a big deal on a very big roundabout with excellent visibility where there's no-one, but that's pretty rare in europe at least.

Rather, what I don't understand is the original argument that roundabouts are bad because the busy direction of traffic has to slow down and gear down unconditionally, whether or not the rare cross traffic is present, so it is then better to have a traffic light there.

The "you need power to accelerate out of danger" is a motorcycle argument (and a pretty flimsy one); in a car, you are not gas-pedaling your way out of anything. Your emergency control devices are brakes and steering, that's it. There are moves that powerful acceleration lets you get away with, and they are all reckless, and often built on the assumption that only you have that acceleration. People are now using their high-torque EVs like this. You will never be in a collision close call caused by someone or something doing something unexpected, where the reaction of stepping on the accelerator is the action that saved the day. Can't deny that it could help run from a tsunami wave or fire or something.

Roundabouts do not need more space.

You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.

Not a civil engineer but as far as I know, the space is part of the point. If you keep the roads straight but just draw a circle in the middle, you don't have a roundabout. It only works properly if the drivers have to curve in and out of it.

You could keep the same space I guess by pinching the roads tighter near the entries/exits but I don't think anyone is talking about that.

The UK has mini roundabouts, which are just a painted white circle on the road: https://upload.wikimedia.org/wikipedia/commons/b/b0/Mini-rou...

Drivers treat them as a normal roundabout by giving way to traffic on the right.

I contest that drivers always treat it the same. They often go through the circle/cut th corner when there is low traffic, and I know at least one mini roundabout where traffic is way less frequent in one direction and the other direction is treated as the "main road" without slowing down.

I mostly like them though.

> You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.

If it's physically possible to "skip the roundabout", if it's just a drawing rather than hard barriers, people here (Spain) will just skip it straight up, unless there is a ton of traffic. I think lots of these driving rules and infrastructure has to take local culture into account, as it differs from "We follow laws like our collective lives depend on it" to "We see laws more like suggestions" depending on the country.

That approach fall down flat on nontrivial traffic amounts. Also it requires an actual hindrance in the middle to enforce compliance, and then bigger vehicles won't be able to turn left.

Drive a school bus through there. Let me know how that goes.

Perfectly fine, actually.

For example, the one at [0] regularly sees bendy buses[1] traverse it without any issues. The trick is that there's an outer ring of asphalt and an inner layer of paving stones: cars the asphalt as it is far more comfortable to drive, but longer vehicles like buses and trucks can let their rear wheels ride over the raised paved area as well.

And yes, it works the same when they are completely round instead of oval - this just happened to be the first clear example I came across.

[0]: https://www.google.com/maps/@52.0660752,5.1198197,3a,75y,21....

[1]: https://busposities.nl/voertuig/cxx_SolarisUrbino18E_9686

The "use more area" needs to be considered in the sense that, designed properly, they eliminate left turn lanes and "suicide lanes" in the center of the road.

Instead, with proper design, you make this "left turn" by going to the next roundabout, going around to follow the road the opposite direction, and then make a right turn.

It's also only true when compared against a no-frills intersection. A two-lane roundabout has better overall throughput than a two-lane intersection with traffic lights. To increase throughput, they usually add turn lanes to avoid cars having to stop in the through lanes -- but the turn lanes require more road surface than the roundabout would have.

This point is so under-appreciated. Roundabouts are really good in some cases, but they're over-utilized in England. Imagine if the US had roundabouts on the interstate and you're getting close.

I think the main problem in England is that there is just too much traffic for too little road. I don't think there is a simple infrastructure solution to that problem.

For example I was going to point out that roundabout completely fail when one direction becomes nose to tail congested but when I thought about local examples, I'd rather take that over a set of traffic lights where it becomes near impossible to get out from one direction if the traffic keeps backing up onto the junction.

> I think the main problem in England is that there is just too much traffic for too little road.

I think Jevons paradox basically guarantees this in both countries. The difference between the two countries (in my theory) is how much responsibility they're willing to place on the drivers. The UK requires much more driver effort for good reasons I suggest in another thread.

> Imagine if the US had roundabouts on the interstate and you're getting close.

What's the problem with a roundabout on the interstate? Obviously it'd have to be huge to account for the speed, so people don't need to change speed too much, but given the right size, it'd work wonderfully.

Nothing depending on your perspective. Mine is a U.S. perspective and a disposition against. They slow things down and require more mental and physical capabilities than the U.S. approach. That’s not accidental or because U.S. people are dumber, it’s just a cultural difference between the countries in terms of driver expectations. I’ve proposed a rationale elsewhere.

> They slow things down and require more mental and physical capabilities than the U.S. approach.

Make the roundabout larger then, and you can keep just about the same speed. How can a roundabout take more mental and physical capabilities and slow you down less, than a stoplight on the interstate? That's very backwards, and not sure what roundabouts you've experienced, if that's the case.

There aren't stoplights on the interstate. That was the point I was making. (It got lost in the follow up.)

But to answer your question, roundabouts always require drivers approaching from all directions to slow down, lookout for cross traffic and assess other drivers' behavior. Stop lights have 2 modes that promise safe passage, and they can be set to prioritize routes.

I have actually seen some roundabout like constructs on parts of the interstate. They're giant, far larger than singular interchanges, and serve to handle multiple branches and belt loops.

Of course, they are augmented by allowing the main direction of travel to bypass the circle and go over/under it

In Sweden they have these huge roundabouts in the countryside. Very large diameter and gentle curves. You can maintain your speed. Awesome. Saves energy too. I assume there's a huge amount of tried and tested traffic innovation that could be directly just copied.

In Spain we have these two, sometimes right outside metropolitan areas, that see a lot of daily traffic, especially around rush hour. They're naturally balancers, if you plan them correctly, makes a ton of sense to default to roundabouts instead of stoplights.

Especially nice for us who plan our car trips based on when there will be the least public traffic out there, as roundabouts don't force you to stop when there is no traffic, and you can essentially keep the same speed with these large roundabouts.

My main two cons with roundabouts are that one, when you have those residential streets where basically every intersection is a roundabout so you get many of them in a quick sequence when you’re going straight all that centripetal force is annoying to deal with.

And the second thing is when you have very large roundabouts, there’s always a bit of chaos involved between shifting lanes from the innermost lane towards the outermost lane because I’ve noticed people don’t enter the roundabout on the right lane, so there’s always a little bit of chaos during the crossover.

> when you’re going straight all that centripetal force is annoying to deal with.

I have literally never noticed this. Are you perhaps speeding through them, instead of properly slowing down?

> there’s always a bit of chaos involved between shifting lanes from the innermost lane towards the outermost lane because I’ve noticed people don’t enter the roundabout on the right lane, so there’s always a little bit of chaos during the crossover.

Multi-lane roundabouts are a completely different beast, and shouldn't be used until both the engineers and the population have gotten plenty of experience with regular one-lane roundabouts. Two-lane ones are just about doable with hard lane separation, but anything more is asking for trouble.

Thank you for mentioning the asymmetrical traffic flow problem. YUMBL even managed to reproduce this using cities skylines, and there's an intersection near my house that's maddening for this. Large two lane circle, downstream from a traffic signal. When the signal is red you can use the circle normally. But when the signal turns green and there's a massive influx of traffic, forget about entering the circle from any point other than the one downstream of the light. Effectively one light controls two intersections

> Small fender benders and sideswipes are much more frequent

All the sources I can find say roundabouts reduce crashes of all types.

Carmel, IN, America's "roundabout capital" has more than tripled in population while reducing overall traffic accidents / year: https://eri.iu.edu/erit/case-studies/carmel-indiana-roundabo....

Small, single lane roundabouts are easy and comfortable to use for cyclists. Upfront the bikelane ends/merges with the main road. Inside a cyclist is as fast or faster than cars. Go with the flow. Use the whole road. The Netherlands have separate lanes for bikes. I think it's unnecessarily complicated in some cases, but it probably works well in general.

The replies to your comment would be a lot funnier if I didn't share a country with some of these people.

You're not gonna "driving culture" your way around a 10:1 volume difference and only a fool would act like you could.

And this is coming from someone who's a big fan of roundabouts (and 4-way stops) on the basis that bad drivers have a worse time at them.

That would generate stronger agreement if the bad drivers’ struggles mostly affected them. Instead, their chaos radiates outward significantly onto those who know how to drive.

> they're also (mostly) worse for cyclists and pedestrians

For cyclists, this is mostly true IMO (depending on implementation), but for pedestrians roudabouts are way better than traffic lights. In the absence of lights, pedestrians have right of way on crossing, so no waiting time, and physically slowed traffic make it safer.

>but for pedestrians roudabouts are way better than traffic lights.

This is ignorant texbook thinking.

As a pedestrian it's far easier to safely time a light, even one without a cross signal, than it is to cross through the un-broken streams of traffic that are entering/exiting a roundabout. You basically have to cross a ways back from the roundabout where the traffic is more like "just crossing a normal road". Which sucks if it's 4-lanes or really busy or fast or there's no sidewalk provision for that (like in the case of roundabouts at highway ramps) and is just a lot more walking to begin with.

For roundabouts that wouldn't be deserving of a light (i.e. the ones replacing 2/4way stops) it's a lateral move.

The point is that traffic streams are not unbroken: when there is a crosswalk and cars are obliged to stop in front of it in the presecence of a pedestrian, then the flow is broken.

Being obliged to stop and actually stopping are not the same.

In the real world, drivers frequently do not stop in the presence of pedestrians.

Just blundering up to crosswalks because "they have to stop, hurr durr it's the law <foams at mouth>" results in a substantially more hazardous pedestrian (and driver) experience than timing your approach and using your body language so that the drivers know what you're gonna do and can take action to hedge against it.

Indeed, this is so, so true.

Especially with heavy traffic, the traffic all slows down, a lot, from the section before the roundabout. Everyone is always in a hurry, so likely 10-25 MPH over the recommended speed (not the speed limit) for the roundabout, and all of them are at a 6 foot following distance.

You are playing with death to step into that. It's no joke. You end up effectively waiting for the upstream light to turn red so traffic can clear and you can cross.

The only solution I've thought of is to put a large grocery cart full of paint buckets at the roundabout for pedestrians to push into the crosswalk without risking their own lives.

> Which sucks if it's 4-lanes or really busy or fast or there's no sidewalk provision for that (like in the case of roundabouts at highway ramps) and is just a lot more walking to begin with.

I mean, it depends on your standards for roundabout. We didn't put highways through town centres so largely highway ramps and pedestrians are mutually exclusive scenarios here. Where pedestrian crossings exist, there's usually (a) an island and (b) 2 lanes prior to the island, splitting to 4 lanes either where the traffic is already slowed or past the island, which makes it much more pleasant than crossing at an equivalent junction. Also as a driver, it means you've cleared the pedestrian area before you have to consider/deal with the cross direction drivers as there's a small waiting area post-pedestrian-crossing/pre-roundabout.

If you're stuck because you already have a highway in your urban core and need pedestrians to safely cross the highway, then you are pretty much limited to overpasses and underpasses.

They are also better for cyclists. Take a look at [0], for example: the pedestrian crossing forces an early stop for cars entering, and there's a neat one-car-sized waiting area for cars leaving. They both reduce the sight angles between the car and a crossing cyclist, so they are quite easy to spot.

[0]: https://www.google.com/maps/@52.0428513,5.0936425,88m

Roundabout cyclist and pedestrian safety is a solved problem, in the Netherlands of course.

Yup I live in an area built around the time 'roundabout fever' has gripped urban planners, so there's quite a few around. To add a few of my personal complaints:

- When there's a low traffic lane merging with a high traffic one, it's either impossible to enter, and you have to wait forever, or there's a traffic light cleverly hidden a couple hundred meters away, as to not break the illusion

- They do work in the middle of nowhere merging two low traffic roads. However for every roundabout you have to slow down which breaks the flow of traffic, and consumes more gas. There's often a string of 5-6 of these things.

- Having to turn to even go straight makes me queasy. Not too bad if there's just 1, but can be super uncomfortable when there's a string of them (which is common)

- 2 lane roundabouts are crazy dangerous and confusing (which is the same). You might understand how they work, but the car behind you might not. Besides due to the geometry of the whole thing, you have to cut across diagonally to car traffic to get to the inner lane.

- There's another kind of 2 lane roundabout, which is less dangerous, but only allows you to turn right from the outer lane. If you're unfamiliar with which kind you're facing, you might be in for a detour. Even if you know, there's often a fight to merge into the inner lane, which is not exactly pleasant or safe.

I guess roundabouts are a niche solution that can work sometimes, but there's a whole internet cult for them, composed mostly of people who don't really live in an area with roundabouts.

> there's a whole internet cult for them, composed mostly of people who don't really live in an area with roundabouts.

Alternatively: it's people who do live in areas which have a lot of them - and well-designed ones at that. Most of your issues boil down to "people aren't familiar with them", which automatically solves itself over time.

There is no such thing as a "roundabout fever", just like there isn't a "traffic light fever". To any halfway-competent engineer, they are just one tool among many.

Roundabouts are also a torment if you have car sickness.

I live in the US and roundabouts simply don't work.

Not much of America's traffic infrastructure works well. Every month, combined with poorly trained motorists, it contributes to another 9/11's worth of fatalities. The infrastructure you think works, kills enough people for a thirteenth month at the end of every year.

They have their downsides, but "It doesn't work in America" is more informative of American motorists than roundabouts

Yeah I regularly drive in France which has terrible drivers (road deaths way above EU average in France) but it's nowhere near as bad as the US.

The one thing people should ponder is this: Germany has less than 3x the number of road deaths (no matter how you count it: per 100 K people, per kilometer, etc.) than the US. And yet every time I'm in Germany I happily drive at 125 mph on the highway (including when I drive to Poland, where most autobahns near Dresde have no speed limit at all whatsoever). And at 125 mph, I'll get overtaken by some cars going proper fast.

So, what, 65 to 70 mph max speed limit vs unlimited speed and three times the deaths: what's the problem?

Note that I'm certainly not advocating for US (or France for that matter) highways without speed limits: drivers are way too bad.

Germany is somewhat an exception when it comes to good and safe driving though, I think they're all afraid the government will take Autobahn away from them if they drive too bad.

It's a huge difference passing through France, having near hit collisions every hour on the highway with distracted French families, arriving to start passing through Germany, and suddenly people actually use their blinkers, drive on the right side, seemingly everyone knows defensive driving, and no one is up in your ass if you're at the speed limit.

Love driving in Germany though, countries should look into how they managed to get the car culture they have. Maybe it helps the Germans invented the automobile and all that comes with that. Probably still there is lessons to be learned from them.

Legislators in the US won't cover the actual costs of road maintenance. Most cities issue long term bonds to finance road construction & repair, but in order to repay those bonds, those states & cities need to constantly grow.

Damage to roads is related to the third power of speed and the fourth power of axle weight.

Huh. You might want to look at how the residents of Carmel Indiana think about this.

https://www.carmel.in.gov/government/departments-services/en...

a city frequently ranked in the top 10 places in the US, also frequently ranked as one of the best cities in the US for cyclists.

I live in The Netherlands and roundabouts work just fine. Other European countries seem to have very similar experiences.

Is there something unique about American drivers or traffic engineers which makes them incapable of handling the concept of a roundabout that I am unfamiliar with?

Thank you so much for putting into words what I have feeling but struggling to verbalize. (Boston area, drive for work.)

There is one more downside, they are easy to get lost in, especially in an unfamiliar area. Apple Maps does an OK job guiding me most of the time, but just yesterday I spent an extra 25 minutes going through the same roundabout 3 times before I went the right direction, and each time I had to drive the wrong way, turn around, and then negotiate the same roundabout again.

Roundabouts are perfect when youre confused, just go around and read all the signs 3 times, then select the exit! :)

> but just yesterday I spent an extra 25 minutes going through the same roundabout 3 times

How big was this roundabout when it took 25 minutes doing 3 victory laps in a roundabout?

You might want to petition your local government to put the signs of the exits before the roundabout, together with exit signs inside of the roundabout, helps a lot to see what exit you should take.

Alternatively, try a different map viewer, both Google Maps and Waze handles roundabouts excellently with zero issues, Apple Maps might still be too new to be useful for daily use.

> How big was this roundabout when it took 25 minutes doing 3 victory laps in a roundabout?

It was clogged probably :)

I've tried Google Maps and Waze already, they were worse.

>How big was this roundabout when it took 25 minutes doing 3 victory laps in a roundabout?

This is explained in the next sentence, I took two wrong exits and had to double back?

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