Are roundabouts actually statistically safer than traditional traffic patterns?

Question

We have had a number of roundabouts installed near us in South Western PA in the past decade, and a quick internet search shows other states doing so as well. This seems to be an almost universally frustrating trend with those I've spoken to.

A quick online search leads to a number of pages such as this one from PennDoT: Road Design > Roundabouts. These pages extoll the safety of roundabouts and quote statistics about how much safer they are than intersections. This sounds great and, if true, I'm on board.

However, my personal experience with roundabouts, even ten years after installation of the first one in our area, involve regular instances of:

drivers switch lanes inside the roundabout at the last minute without looking because they are unclear which lane to be in, or how to properly get to the inner lane
drivers fail to yield when entering the roundabout since they're used to most cars flowing straight
drivers slow nearly to a stop in confusion while they try to understand how to use the roundabout (hopefully this will disappear eventually)

I experience at least one of the above almost every visit to a roundabout. There have also been at least 2 accidents that I've heard of in our local roundabout, despite it being a medium-low traffic road. This makes me question whether the statistics being presented are cherry picked or presented out of context to appear to support an untrue premise.

Are roundabouts actually safer than traditional intersections, and I'm just seeing issues caused by the adoption of the new and unfamiliar? Or are these statistics false or misleading?

EDIT

Thank you, all, for the wonderful answers.

Since the question has been asked a number of times, I wanted to post a link to the particular roundabout that prompted my question: https://www.google.com/maps/@40.2038168,-80.1263559,151m/data=!3m1!1e3

Ironically, the day after accepting the answer about them being safer, I had to slam my brakes to avoid being hit by an entering car that ignored the yield and just continued through at 30+ mph. The universe is messing with me again...

This question is a bit too broad at the moment, because there are so many different types of intersection, and no-one is saying roundabouts are appropriate for every one. The claimant is saying (a) better than lights [still broad] and (b) better than the previous stop-sign/lights for 26 roundabouts in Pennsylvania. Can we limit the claim appropriately? — Oddthinking, Sep 09 '22 at 05:24
Reminder: Comments are for clarifying and improving the question, not discussing your opinions on traffic around the world. — Oddthinking, Sep 09 '22 at 05:25
Can you define "safer"? I will gladly accept 100 more crashes with property damage to save 1 life so te me a huge increase in crashes with a reduction in deadly crashes falls under "safer". If you just count any kind of collision or accident, no matter their consequences the result will be completely different. Moreover as @Oddthinking is saying there is no single type of "intersectin" and also there is no single type of roundabout, so it's likely that some kind of roundabouts are worse and others are extremely better (at least coming from the EU where they are way more common...) — GACy20, Sep 09 '22 at 07:38
Welcome Hot Network Question Readers: Here at Skeptics.SE, we actively DO NOT WANT your opinions or your anecdotes in the comments. Comments are for clarifying the question. Answer boxes are for fully-referenced answers. — Oddthinking, Sep 10 '22 at 06:31
'Safer per person-mile' is not the same as 'safer per person-hour' is not the same as 'safer per person-trip' is not the same as 'safer per intersection-hour'. (For an illustration of this: changing a road to have an enforced speed limit of 1 furlong/fortnight would likely make it safer per person-hour, but not per person-mile, and would likely cause many people to avoid said road, which would make it safer per intersection-hour but which could have mixed effects on safety per person-trip depending on the alternatives people end up using.) Could you please clarify which of these you mean? — TLW, Sep 10 '22 at 21:52
@TLW: We should focus on what the claimant means in their claim, rather than what the OP's personal definition is. — Oddthinking, Sep 11 '22 at 01:54
Sure; I would argue that one common "false or misleading" use of statistics is to claim something general and then provide statistics that only show one specific subcase is true - such as claiming something is "safer" in general but providing statistics that only show it is safer per intersection-hour. (If change X reduces the accident rate per intersection-hour (while increasing the accident rate per person-mile), is that valid evidence backing the claim that it makes it "safer"?) — TLW, Sep 11 '22 at 02:18
When I see a roundabout I don't like, I get in it and go round and round and round like Chevy Chase in one of his Vacation movies.... As far as I can tell, it's perfectly legal to perform a denial of service attack in a roundabout. — Michael, Sep 11 '22 at 19:17
The main reason for roundabouts is that they are the most efficient system for junctions, within quite a large range of traffic volumes. — User65535, Sep 12 '22 at 11:48
@Michael [No it's not](https://law.stackexchange.com/questions/81615/is-it-legal-for-a-group-of-drivers-to-completely-fill-a-roundabout) — pipe, Sep 12 '22 at 16:07
This is the same syndrome we get with Michigan Lefts. People react *emotionally* to how they are different. But they never compare *with how it was **before*** - sitting and waiting for 2-3 minutes while it cycles through 8 different phases. Michigan Lefts only have 2 phases and it's easy to synchronize signals, so you spend little time at a red light. Walk buttons are unneeded since peds only have to dodge right-on-red folks. — Harper - Reinstate Monica, Sep 12 '22 at 22:18
Regarding the linked roundabout in the edit, from the angle the streets enter at, it seems easy not to notice that it's a roundabout. Compare with a few roundabouts from Europe: [1](https://www.google.com/maps/@47.6252702,7.6134389,132m/data=!3m1!1e3), [2](https://www.google.com/maps/@47.6221519,7.613768,115m/data=!3m1!1e3), [3](https://www.google.com/maps/@47.90428,8.1564844,156m/data=!3m1!1e3), [4](https://www.google.com/maps/@47.9078744,8.1597497,191m/data=!3m1!1e3), [5](https://www.google.com/maps/@48.0220803,7.8510378,64m/data=!3m1!1e3)... — Kyralessa, Sep 23 '22 at 13:53
...in the European roundabouts, you can't avoid seeing the circle in the middle. Whereas with the one you've linked to (as well as the one just to the north of it), the roads enter at such a sharp angle that you can fail to notice you're entering a roundabout. This may subtlely encourage cars to enter at speed instead of waiting their turn. This angle also appears to make it harder for entering cars to see traffic already in the roundabout; they have to turn their heads much more sharply, possibly more than 90°, to see cars from the left. — Kyralessa, Sep 23 '22 at 13:58

score 94 · Accepted Answer · edited Sep 11 '22 at 01:54

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Here is a study of traffic safety at roundabouts in Minnesota. In this study they looked at all roundabouts in Minnesota, and look at the recorded crash data at these sites, comparing the data before the construction of the roundabouts to that after the construction.

The findings of this technical report both confirm the increased safety of roundabouts and your anecdotal report of increased incidents at round abouts. In particular they found

a significant decrease in the number of serious accidents that were fatal (-86%) or lead to serious injury (-83%)
an increase in the number of "property damage only" crashes, which were up 50%.
a slight increase (+15%) in the overall number of crashes.

The explanation for this comes from the fact that the nature of crashes at roundabouts is very different from that at traditional crossings. Roundabouts experience a decrease (-35%) in the number of right angle collisions (typically the most dangerous crashes), while experiencing in increase of the number of sideswipe (+681%), and "ran-off road" incidents (+272% or +373% depending on the side of the road).

EDIT: In the comments @Oddthinking makes the fair point that this data mainly shows that placing a roundabout can make a dangerous intersection safer, but it does not necessarily tell us whether a roundabout is a safer option than other improvements one could make to an intersection. The report does actually contain data comparing different intersection types (this time using data from the 2015 Minnesota Intersection Toolkit, based on 5 years of crash data from 2011-2015.

Traffic Control Device	Crash Rate	Fatal and Serious Injury Crash Rate
Urban Thru-Stop	0.18	0.33
Rural Thru-Stop	0.25	1.05
Signal - Low Volume/Low Speed	0.52	0.42
All-Way Stop	0.35	0.57
Single Lane Roundabout	0.32	0.31
Signal - High Volume/Low Speed	0.70	0.76
Signal - High Volume/High Speed	0.45	0.48
Unbalanced Roundabout	0.76	0.15
Dual Lane Roundabout	2.18	0.00
All Roundabouts	0.51	0.24

And here's a color-coded version:

While roundabouts (particularly dual lane roundabouts) show higher overall crash rates than other intersection types, they show lower rates of fatal and serious injury crashes. This is consistent with the other findings. Of course, there could still be some sort of selection bias due to the fact that certain solutions are built in certain situations based on where they would best fit.

Source: Leuer, Derek, and Safety and Technology Minnesota. Dept. of Transportation. Office of Traffic. “A Study of the Traffic Safety at Roundabouts in Minnesota,” October 30, 2017.

edited Sep 11 '22 at 01:54

Kyralessa

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answered Sep 08 '22 at 21:33

TimRias

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A source of bias in this approach is that the intersections were not randomly selected, but very likely selected for upgrade because of a history of accidents or congestion. If roundabouts hadn't been an option, they may have had lights or other safety measures installed. The comparison should be roundabouts versus similar-priced alternatives (e.g. lights), not roundabouts versus unimproved dangerous intersections. – Oddthinking Sep 09 '22 at 05:21
@Oddthinking Where did you see that in the report? I can't find it. – barbecue Sep 09 '22 at 05:26
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@barbecue That's the problem. They say nothing about the "control group", making the report unconvincing. At the end they quote the crash rates for alternatives (lights) from "the 2015 Minnesota Intersection Toolkit", but - again - any decision to upgrade an intersection is predictably *very* *far* *from* *random*. – kubanczyk Sep 09 '22 at 07:38
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I see the problem that the table has different throughputs of solutions. For example, crossing with traffic lights has higher average throughput than a single lane roundabout. So, if you drop speed in such crossings to have the same throughput as a roundabout (eg by speed bumps), would you still see net benefit in roundabout safety over traffic lights? If you do, then yeah, roundabouts are great. If you don't, the main point to improve safety is simply the need to drop speed at intersections somehow and roundabouts are one possibility but perhaps not the best one. – Zizy Archer Sep 09 '22 at 09:03
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Seems like a single-lane roundabout is better than an all-way stop on both rates? Not sure which way the throughput goes on that one, but probably in favour of the roundabout as well... – Jiří Baum Sep 09 '22 at 11:02
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"While roundabouts (particularly dual lane roundabouts) show higher overall crash rates than other intersection types" - the table shows single-lane roundabouts having *lower* overall crash rates than every intersection type except thru-stops, which doesn't quite match what you wrote here. – NotThatGuy Sep 09 '22 at 12:05
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Maybe this is a cultural difference in terminology, but having not been able to find an explanation online - what is a "Thru-Stop"? – Zibbobz Sep 09 '22 at 12:32
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I think Thru-Stop is probably in contrast with All-Way Stop, in which all (usually four) directions must stop before entering the intersection. Presumably in a Thru-Stop, only two of the four directions must stop before proceeding, and the other two directions go through without stopping. Rarely these are marked with signs "Cross Traffic Does Not Stop" (the presence of which sign may be an indicator that a thru-stop may not be the best choice for that intersection). – shoover Sep 09 '22 at 12:57
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Also the "Dual Lane Roundabout" stats look like they're derived from much smaller numbers of journeys than everything else: the incident rate is abnormally high yet barely affects the low "all roundabouts" average (and it's striking there hasn't been a single fatal accident yet). Sounds to me like there's only one or two "Dual Lane Roundabout"s in the area, recently built, and local drivers are still getting used to it. If true, their stats are almost certainly not statistically significant or stable, and I'd advise not drawing conclusions from those until there's more data. – user56reinstatemonica8 Sep 09 '22 at 13:18
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@user56reinstatemonica8 Dual lane roundabouts account for about 10% of the total traffic volume through roundabouts in the data. But they are low in number (only 6 out of 144 totals roundabouts). – TimRias Sep 09 '22 at 13:25
curious they do not include "at grade" clover leaf. Many New Jersey roundabouts (e.g. Racetrack Circle on rt 70) were replaced with this type to alleviate the "insane" traffic backups and accidents. Not a clover leaf in the elevated highway sense. – Yorik Sep 09 '22 at 14:59
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Cloverleaf takes up too much area. – shoover Sep 09 '22 at 15:48
@JimmyJames I live in a city that has only a few roundabouts, but the signage varies, in one case explicitly commanding traffic already in the circle to yield to entering traffic, and in another case explicitly commanding entering traffic to yield to traffic already in the circle. So "the rule" isn't "the rule" everywhere. – shoover Sep 09 '22 at 15:51
@shoover Priority to the circulating traffic is one of the key aspects of the [_modern roundabout_](https://en.wikipedia.org/wiki/Roundabout#Modern_roundabout). Basically all new roundabouts are designed that way. The older variant with opposite priority is sometimes called _traffic circle_ to make a distinction. According to Wikipedia "Many old traffic circles remain in the northeastern US.". So maybe the first circle you are thinking about is a relic from a previous traffic planning paradigm? – jkej Sep 09 '22 at 17:51
Nope, all of these were built in the last 10-20 years in a car-centric city in the Sun Belt, probably designed by traffic engineers with no prior experience with traffic circles / roundabouts. – shoover Sep 09 '22 at 18:44
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@shoover So there's some precedent though. I wasn't aware of that. It reminds me a bit of a wedding reception I attended where food was laid out on a circular table. Everyone was hungry and rushed to the table. Then everyone turned and waited for the person in front of them to move. It took a couple minutes before people started realizing they were standing in their own way. – JimmyJames Sep 09 '22 at 20:09
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The data matches how Germany builds roundabouts: We barely build Dual Lane Roundabouts, only smaller ones. If the traffic is to dense and would require a second lane, we stick to traffic lights. – usr1234567 Sep 10 '22 at 05:01
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Note for anyone curious about the units of the "Rate" columns: page 10 of the document linked in this answer says the "Crash Rate" is crashes per *million entries* to the intersection, and "Fatal and Serious Injury Crash Rate" is the sum of fatalities and serious injuries per *one hundred million entries* to the intersection. – X Goodrich Sep 10 '22 at 08:31
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An interesting factoid from the paper: Several of the serious crashes on roundabouts were impaired drivers crashing into the middle of the roundabout. Probably wouldn't have happened on a straight intersection, unless they hit a car. So more dangerous to drunk drivers, safer for everyone else. – Cyrus Sep 10 '22 at 09:26
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Note also that there's a factor of familiarity. Without evidence I would assert that the average american is signficantly less familiar with traversing a roundabout that the average Brit/European. And (again without evidence) it seems fairly self-evident that roundabouts are harder to safely navigate when you're not familiar with the concept than other junction types. Thus one might conclude that the safety of each roundabout would increase as they become more common. – Brondahl Sep 10 '22 at 09:57
`an increase in [...] crashes, which were up 50%` is the opposite of "safer". The question's not about deadly accidents but accidents in general. – Haukinger Sep 10 '22 at 11:32
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@Haukinger the question is about safety not accidents. Severity of incidents clearly is a factor. The 50% up were incidents where nobody was injured, and there was only property damage. Such incidents maybe undesirable but they are not dangerous. – TimRias Sep 10 '22 at 18:54
@TimRias You can only count accidents, not an abstract concept of safety, thus when talking about "statistically safer", one necessarily means "statistically less accidents". The question contains no limitation on accidents where people are bodily hurt or "only" lose lifetime or property. You can weigh accidents differently, though, like "hours of lifetime lost" which can be made to include death, hospital and even property damage (by multiplying with "hours of life/dollar earned") – Haukinger Sep 10 '22 at 20:08
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@Haukinger When talking about safety, accidents where no one is injured are irrelevant. – TimRias Sep 10 '22 at 21:44
@TimRias I'm no native speaker, so there may be subtlety of which I'm ignorant. The definition of "safety" at webster reads "the condition of being safe from undergoing or causing hurt, injury, or **loss**" (emphasis mine). It seems strange to me, to say the least, to say "hey, this type of intersection's totally safe!" when noone ever gets hurt there but all cars are destroyed. – Haukinger Sep 11 '22 at 10:50
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I don't understand how to interpret the table. The "Fatal and Serious Injury Crash Rate" is higher than the "Crash Rate" for several of these intersection types, so those numbers can't mean what they sound like to me. Can you add the definitions? – ruakh Sep 11 '22 at 21:28
Why do we care about the cost of the intersection @oddthinking? Are you from a country with a low value on human life? – Harper - Reinstate Monica Sep 11 '22 at 21:57
@Haukinger There are lots of ways to define a measure one might plausibly call "safety" that is relevant to this topic. The question doesn't mandate one; it's just as misleading to assume that it *must* be defined as a naive count of accidents (disregarding actual harm to people) as it would be to assume that it *must* be defined as a naive count of serious injury/death, disregarding any other accidents. Fortunately the answer doesn't mislead in either of these ways; it quotes the effects on both all accidents *and* accidents causing serious injury/death. – Ben Sep 12 '22 at 03:17
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@Haukinger And even if you're interested in "safety from loss", merely counting the accidents would be pointless for that purpose too. We don't have data here, but I'm pretty sure that since the actual effect of roundabouts on reducing serious injury and death is dramatically lower speed/force of almost all collisions that do occur (even though there are more of them), then you would also find less average property damage. Crashes that mangle people also mangle cars. So you'd probably see similar results if you used "accidents causing at least X thousand dollars damage" as the break-out. – Ben Sep 12 '22 at 03:22
@Harper-ReinstateMonica: I don't know how to answer that without gesturing vaguely at the field of economics. The richest countries in the world still have limited budgets to spend on road-safety. Perhaps we should go to chat? – Oddthinking Sep 12 '22 at 03:58
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One thing this data doesn't seem to address is the effect on different modes. For example a roundabout could have double the serious injury or death rate for cyclists while still appearing safer because motorist are only likely to suffer car damage in collisions. They also tend to be worse for pedestrians particularly those with more than 4 exits. The point I am trying to make is that it is overly simplistic to say "roundabouts are safer" even if some study appears to back that up. It's worse if "safer" is used as a stand-in for "better". – Eric Nolan Sep 12 '22 at 14:48
@ruakh I'm pretty sure those numbers are relative to a control--probably the original accident rate. – Loren Pechtel Sep 13 '22 at 03:22
@Ben `it's just [...] misleading to assume that it [...] must be defined as a naive count of serious injury/death` that's exactly what @TimRias does in this answer and in comments, and that's what provoked my comment. – Haukinger Sep 13 '22 at 05:59
@EricNolan exactly this. If "safer" were "better", we'd just scrap all roads and cars and stay at home, no traffic at all is ultimately the safest traffic. Thus all trying to make traffic better by making it safer is (kind of) moot, one needs optimise for throughput and individual trip duration - accidents are are only undesirable insofar as they disturb traffic. – Haukinger Sep 13 '22 at 06:03
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@Haukinger I don't agree with that at all. Someone who thinks the only metric for road design is maximising speed and throughput for cars should be kept as far away from road design as possible. The point I was making was that doing something like removing almost all pedestrian crossings would mean less accidents but it is not better for those people who have to walk 30 minutes to cross the road. – Eric Nolan Sep 13 '22 at 09:15
@EricNolan I didn't say `for cars` - your example `removing almost all pedestrian crossings would mean less accidents but it is not better for those people who have to walk 30 minutes to cross the road` essentially says the same thing: `optimize for speed instead of safety` - live with an accident now and then to get a huge reduction in travel time for everyone. – Haukinger Sep 13 '22 at 11:32

score 47 · Answer 2 · edited Sep 10 '22 at 09:50

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Germany started to reintroduce roundabouts in 2000, so quite a lot of research has been done, and there is plenty of experience.

The German "Bundesanstalt für Straßenwesen", federal road research institute, conducted a study about roundabout safety in 2021. The results are published in https://bast.opus.hbz-nrw.de/opus45-bast/frontdoor/deliver/index/docId/2512/file/V343_BF_Gesamt.pdf. The document is in German, but has an English abstract and summary on pages 3-9.

They state "Literature consistently finds a higher level of safety at roundabouts compared to other types of intersections on rural roads." and "severity of accidents is lower at rural roundabouts then [sic] at other types or rural intersections", then continue with evaluating the main dangers and constructive measures to avoid them.

The UDV (Unfallforschung der Versicherer), an accident research organization funded by Insurers, came to a similar conclusion, but stated that there are some problems with cyclists, in a report compiled in 2012 (https://www.udv.de/udv/themen/sicherheit-inneroertlicher-kreisverkehre-75470, in German). The research was specifically done to evaluate roundabouts in towns, as they said

Kleine Kreisverkehrsplätze gelten außerorts zu Recht sowohl in Deutschland als auch im Ausland als ausgesprochen sichere Verkehrsanlagen. Unterschiedliche Untersuchungen ... kommen jedoch zu dem Ergebnis, dass innerorts Sicherheitsprobleme mit dem Radverkehr auftreten können.

"Small roundabouts outside of towns are considered, rightfully, in Germany and abroad, as very safe traffic installations. However, various examinations conclude that in towns there may be safety problems with cyclist traffic" (my translation).

They analyzed all accident counts in roundabouts in the state of Nordrhein-Westfalen and each individual accident at 100 selected roundabouts in all of Germany, and they used video to analyze driver behavior at 10 roundabouts. (As they are run by insurers, they have access to detailed accident reports whenever insurers are involved.) As a result, they came to the conclusion that

Es stellte sich heraus, dass Kreisverkehre auch innerorts ein höheres Sicherheitsniveau erreichen als signalisierte oder unsignalisierte Knotenpunkte. Während Kraftfahrzeuge und Fußgänger vom Sicherheitsgewinn deutlich profitieren, kann allerdings die Sicherheit für den Radverkehr nicht immer verbessert werden.

"The conclusion was that, also inside towns, roundabouts reach a higher level of safety compared to crossings (with or without traffic lights). While motorized vehicles and pedestrians profit clearly from the safety gains, the safety for cyclists cannot always be increased".

So, both studies, conducted by organizations whose main function is road safety, come to the conclusion that

Literature commonly says roundabouts are safer than other types of crossings
their own research confirms this
there are rules and best practices that have to be followed to eliminate common causes of accidents; if those are omitted, safety may be reduced.

edited Sep 10 '22 at 09:50

phoog

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answered Sep 09 '22 at 07:38

Guntram Blohm

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The problem with using data from Germany is that in general the level of driving proficiency and discipline in Germany is much higher than in the US. It could be that roundabouts are safer when used by competent road users, but unsafer when the road users do not know what to do at a roundabout. – TimRias Sep 09 '22 at 07:48
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@TimRias It's also possible that the level of driving proficiency in Germany, which you claim to be higher (source?), is due to road users having used roundabouts for twenty years. In places where roundabouts were introduced more recently, users may still be in the learning curve. In particular, newer generations of road users may have an advantage over people used to "just driving through", for example. The US may reach similar results in a decade. – Simone Sep 09 '22 at 07:57
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@Simone Every driver in Germany has at least 12 * 45 minutes of driving instruction by a professional driving instructor (this is the legal minimum, the typical time is probably double that) and has to pass a practical driving test (which is not entirely trivial to pass). So the minimum level of driving lessons is much higher in Germany than in the US as far as I understand the US system. – Mad Scientist Sep 09 '22 at 08:22
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@MadScientist this, and also you can't drive alone until you're 18 - but you can drive at 17 after passing the test if there's an experienced driver, usually a parent, in the passenger seat. So while the typical high-risk-little-experience driver in the US is 16 with a few hours of driving, in Germany they're 18 and have had one year of supervised experience gain. – Guntram Blohm Sep 09 '22 at 08:27
@MadScientist I don't know enough about US driving license tests to comment on that, so I'll take your word for it. Instruction and training alone don't necessarily make the godd/safe driver, but I see what you mean. – Simone Sep 09 '22 at 09:08
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@MadScientist The whole "europeans drivers are better" is false. True, novel drivers may be much better in Europe (at 18yo and after intensive proffessional classes) than in the US, but after a couple years of experience driving I expect US drivers to be equal or better than europeans, and those are 95+% of the drivers out there. I got my driver licence at 18, and in my first 10 years as a driver I can count the number of times I drove a car with the fingers of my hands - we use public transport; they drive everywhere. I've driven in the US, and didn't found US drivers any worse than here. – Rekesoft Sep 09 '22 at 09:30
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I think comparing driver "quality" is a red herring when looking at roundabouts. European drivers encounter them all the time wherever they go, so they're routine and everyone knows what to do. American drivers are no less capable of learning them, but even if they are experienced on roundabouts, they still have to deal with other drivers that are not because roundabouts are rare. That makes for more unpredictable situations and thus crashes. – Cyrus Sep 09 '22 at 10:01
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@TimRias Re German driving proficiency: it doesn't matter and isn't a factor _for this question_. The question is are roundabouts statistically proven to be safer. – CGCampbell Sep 09 '22 at 12:06
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Could it be that roundabouts decrease speed, but not for cyclists who go relatively slow anyway, so cyclists wouldn't have more safety due to speed decrease? – gnasher729 Sep 09 '22 at 12:12
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@CGCampbell As I said, the safety of roundabouts can potentially depend on the proficiency of the users (and other cultural factors). Consequently, proof that roundabouts are statistically proven safer in Germany, may not translate to roundabouts in the US being safer. – TimRias Sep 09 '22 at 13:06
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First of all, drivers *everywhere* are terrible at driving. They are always running into stuff and each other. The idea that some country's drivers are "better at driving" than another is ridiculous. Instead, any accident disparities among countries should be put squarely on the traffic controls and common vehicles used. That being said, from a person whose driven in numerous countries on 4 continents, Americans are by far the most *polite* drivers, which explains their hesitancy to slip into a roundabout and "cutoff" somebody, even though that's what you're supposed to do. – Sep 09 '22 at 13:20
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@MadScientist My driver's instruction in the USA was 12, 2 hour courses, and 12, 1 hour instructed drives. Then both a written and driving test must have been passed before earning the license. I was under the impression this was the minimum requirement in my state. However, I was 16, and I'm also under the impression that *anyone* over 18 need only take the written test to be licensed (*whelp*). – Sep 09 '22 at 13:25
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@TimRias I disagree. Let's make your statement about German drivers factual. (I don't believe it, but let's just assume for the minute it is fact.) Now, compare those German driver's safety records on roundabouts with non-roundabout intersections. Are roundabouts safer than non-roundabouts? When PA decided to use roundabouts, that is what they would have done. Picked a locality, whether it was Germany, or Minnesota is not relevant, as long as the statistical comparison from R to non-R was all in the same locality. Are R's safer. German abilities don't mater. R to non-R do. – CGCampbell Sep 09 '22 at 13:35
@gnasher729, in Ontario Canada at least, cyclists are encouraged to use the pedestrian crossings. To me that seems like a recipe for disaster. Even as a pedestrian I don't use the crossings (it's safer to jay-walk, not assuming right-of-way, further up the block). As a cyclist I drive simply as if I were in a smaller, sometimes slower, car. I feel far safer zooming around with the traffic than I would if I cut across it expecting it to stop for me. – Ray Butterworth Sep 09 '22 at 13:38
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@fredsbend I don't think you're "supposed" to cut people off in a traffic circle/roundabout. My understanding is that you should wait for a safe gap before entering the circle. – Onyz Sep 09 '22 at 14:14
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@Onyz I believe it varies by location. In the UK, priority is to drivers already on the roundabout so you should not cut anyone off, but in France I believe priority is to drivers entering the roundabout (this is at least true of the Place de l'Etoile around the Arc de Triomphe) – Tristan Sep 09 '22 at 15:44
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@Onyz I put cutoff in quotes, because the American interpretation is very broad. Americans will complain about a "cutoff" that a European never would. A very polite driving population, but cause issues at roundabouts. – Sep 09 '22 at 15:55
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@MadScientist you’re committing the fallacy of credentialism by assuming that professional German courses are necessarily much better than real world experience which that rapidly accumulates after you get your license. Germany primarily has strict license laws due to lobbying efforts, not because it’s actually important for safety. – JonathanReez Sep 09 '22 at 16:31
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@MadScientist There is no such thing as a "US system" for licensing. There are, in fact, 56 different such systems in the US, one each for the 50 states, 5 territories, and Washington, DC. Every jurisdiction sets its own training, experience, age, and examination requirements for obtaining a license. Furthermore, there are also 56 different sets of driving laws, signage laws, enforcement laws, and penalties. Many rules are similar from state to state, but with small differences; for example, all states have seatbelt laws, but only some states let police pull you over for not wearing one. – A. R. Sep 09 '22 at 18:04
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@Tristan I believe you are wrong about the UK/France difference in terms of priority. If Place de l'Etoile still gives priority to entering traffic, it's because it's old, not because it's in France. Basically all modern roundabouts worldwide are built with priority for circulating traffic. Some countries may have totally phased out the old priority rule though. – jkej Sep 09 '22 at 18:08
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@JonathanReez – in Slovakia (in many things we copied German system), the level of examinations to get a driving license is set that (bottom) 30% of general population could **not** pass them. This was confirmed to me at consultation with traffic psychologist. In U.S., such a restrictive quota probably won't work because the current setting of expected mobility is not ready for this. In Europe, driving license is not neccessary for living that much due to quality coverage by public transportation which is also cheaper. Everyone should mind that bottom 30% cutoff when comparing Europe and U.S. – miroxlav Sep 09 '22 at 21:17
@MadScientist Another thing to note is some of the basic laws can differ from state to state. Things like making a right hand turn on red light in some states it is allowed and others it isn't, or if u-turns are allowed at intersections. Other things such as if traffic on an interstate/high way has to move to the left to let traffic entering from the on ramp change from state to state. – Joe W Sep 09 '22 at 22:48
@TimRias I'm fairly sure that the competence difference is not there, but familiarity and experience do play a role. Commuters can probably handle all types of intersections safely, but noobs have problems. The first roundabout along my commute was built about a decade ago, basically to feed traffic to-and-fro a freshly constructed shopping center. After the first couple of weeks the rush hour commuter traffic was unproblematic. Rural visitors to Ikea on weekends on the other hand... – Jyrki Lahtonen Sep 10 '22 at 06:37
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I'm a bit surprised by the finding re: cyclists. May be my point of view is different because locally the small roundabouts are for motor traffic only, and bike riders like yours truly share a separate paved path with pedestrians. In a more urban setting our roundabout handle intersections of highways/arterial roads, where no sane bicyclist would mingle with the cars anyway. Of course, Germany vs. Finland is at least one order of magnitude difference in traffic density. – Jyrki Lahtonen Sep 10 '22 at 06:42
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In my experience roundabouts are an absolute nightmare for cyclists. I've lived in many cities in New Zealand and Australia where roundabouts are frequent and cycle lanes are not. The main issue is often smaller roundabouts have a chicane which forces cyclists to merge from the shoulder into the road lane. Plus drivers tend to approach roundabouts at much higher speed than stop/give way intersections, glance to see if there are cars approaching and if not drive out. I've been hit twice on roundabouts by cars not looking before they enter. – David Waterworth Sep 10 '22 at 07:09
@DavidWaterworth where I live a pretty bad roundabout for cyclists was improved a few years ago. Here's what it was like before (streetview link): https://goo.gl/maps/oebfhYE2EvVUJe13A and here's what it's like now: https://goo.gl/maps/FaJpPUv4AXd6oSLA7 . It's a lot safer now. – Aaron F Sep 10 '22 at 10:18
As a cyclist, roundabouts are truly awful places. One good thing about high-volume roundabouts is they cost a lot and use a lot of space, so installing cyclist underpasses at each road is not an enormous extra cost. – Criggie Sep 11 '22 at 19:43

score 5 · Answer 3 · answered Sep 11 '22 at 05:22

When talking about "safety", you could mean one of many metrics. Some common ones include:

Deaths per day per intersection.
Accidents per day per intersection.
Deaths per car entering the intersection.
Accidents per car entering the intersection.
Deaths per person-mile traveled.
Accidents per person-mile traveled.
Deaths per person-hour traveling.
Accidents per person-hour traveling.
Deaths per person-trip.
Accidents per person-trip.
Person-lifetimes per person-mile traveled.
Person-lifetimes per person-trip.

Now consider three alternatives:

Intersection A lets through 2 vehicles per unit of time, on average. Each vehicle takes ten units of time and distance for its trip. One in a million vehicles crash; 1 in ten vehicle crashes result in a fatality.

Intersection B lets through 1 vehicle per unit of time on average. Each vehicle takes a hundred units of time and four units of distance for its trip. Two in a million vehicles crash; one in forty vehicle crashes result in a fatality.

Intersection C... no-one uses intersection C, because a vehicle would require a literal lifetime to go through it, and so people have changed their routes, instead taking a thousand-unit of time and distance to avoid it.

Now. Which of these is safest?

Intersection C wins for deaths and accidents per day per intersection, fairly trivially (no-one ever uses it). Intersection C loses for person-lifetimes per person-trip or person-mile, again fairly trivially.

Intersection A wins on accidents per car entering the intersection. Intersection B wins on deaths per car entering the intersection.

Intersection A wins on deaths per person-mile traveled. Intersection B wins on deaths per person-hours traveled.

Given all of the above, it would be misleading to say that intersection B was safer than intersection A, even if you provided (correct) backing statistics showing that intersection B wins on deaths per car entering the intersection. It would also be misleading to say that intersection B was less safe than intersection A, even if you provided (correct) backing statistics showing that intersection A wins on deaths per person-mile traveled.

So. Coming back to your question:

Are roundabouts actually safer than traditional intersections, and I'm just seeing issues caused by the adoption of the new and unfamiliar? Or are these statistics false or misleading?

Roundabouts are safer by some metrics than traditional intersections; these statistics are arguably misleading for the claim that roundabouts are safer in general.

Roundabouts tend to be superior w.r.t. deaths per day and deaths per vehicle, and you'll see many statistics that show this (e.g. your link, or https://rosap.ntl.bts.gov/view/dot/35084 , etc.)

Table one of https://dr.lib.iastate.edu/server/api/core/bitstreams/6d1e271e-1a94-4b98-afbb-95f62e805832/content shows 5.6 fatal accidents per billion vehicles entering the intersection for high-speed signals, and 1.9 fatal accidents per billion vehicles entering the intersection for high-speed roundabouts. This is a difference of 3.7 fatal accidents per billion vehicles in favor of roundabouts.

Roundabout accident rates are often higher per vehicle, especially in unbalanced and multilane roundabouts. (e.g. the Minnesota paper with "Many of the [unbalanced roundabout] sites have seen an increase in the frequency of crashes, and the overall total crash rates. However, unbalanced roundabouts are achieving a noticeable reduction in fatal, serious injury, and other injury crashes.").

It is difficult to directly find comparative statistics on the other metrics for roundabouts versus signaled intersections. You generally have to combine multiple statistics and hope you haven't introduced bias in the process.

There are situations where roundabouts are slower than alternatives. (There are also situations where a roundabout is faster than alternatives.) (To disambiguate: 'slower' in the sense of 'taking longer for a specific vehicle to get through the intersection'.) Consider the intersection of a high-traffic high-speed road and a low-traffic road, for instance. A controlled intersection can be set up with traffic sensors, where the light normally stays green for the high-traffic road, only changing when a car actually shows up on the low-traffic road. This results in most cars not having to slow down, and very little average delay. Meanwhile, a roundabout will always require cars to slow down and turn, regardless of how much traffic is on the sidestreet. This shows up as increased average intersection control delays.

Compare table 3 of https://onlinepubs.trb.org/Onlinepubs/circulars/ec083/42_Kaubpaper.pdf (the first paper I could find that included estimated average delay for both a signal and corresponding roundabout, if you're wondering). In this case, moving from a signal to a roundabout increases estimated average delay from 11.9/15.0 seconds to 20.6/33.4 seconds, or an increase of 8.7/18.4 seconds in AM/PM, respectively.

Assume as a ballpark guess that average vehicle occupancy is roughly the same as average fatalities in a fatal crash, and so 3.7 fatal accidents/billion translates to ~3.7 fatalities per billion vehicles entering the intersection. (I'd love to hear about better numbers here.) Meanwhile, US life expectancy in 2019 was 78.8 years, or ~700 thousand hours. 3.7 person-lifetimes per billion vehicles entering the intersection translates to about 9.2 seconds.

You'll note that 8.7 < 9.2, but 18.4 > 9.2. So in this case, the roundabout won in person-lifetimes per transit in the morning, but lost in the afternoon.

(There are several issues with this analysis. The average age of people driving is greater than zero. On the other hand, time spent in transit is arguably not completely wasted. On the other other hand, average vehicle occupancy is more than one. On the other other other hand, average fatalities per fatal crash is also more than one.)

Tetsujin · Answer 4 · 2022-09-12T11:35:48.827

This could depend on your definition of 'safer' - fewer accidents, or fewer injuries/deaths.

If you watch YooToob's 'dash cam' compilations, you quickly spot that Americans can't use traffic lights & Brits can't use roundabouts. What you will also see is the enormous difference in how serious the results are.

By their very nature, many of these videos use the most spectacular footage they can find, which makes them a biased view; but of the ones who concentrate on US footage, the sheer number & carnage resulting from 40mph+ T-bones & 'turning left against a straight-through light' incidents is remarkable. [No-one asked for my opinion, but I actually think this is a result of having the traffic lights so high up, well out of the natural sightline.]

Comparatively, the British roundabout incidents are often someone changing lanes foolishly, or entering when unsafe. These usually result in either some heavy braking & horn blowing, or some dented metalwork. They don't end in lamp posts & telegraph poles down, cars spun right off the road in tangles of twisted metal.

By my definition, that already makes roundabouts 'safer'. There are fewer deaths and serious injuries.

One thing we have in the UK is a lane system, where if you start in the correct lane, you will naturally be fed out into the correct exit. This can make a huge difference in big roundabouts, where you can't even see your exit from the entrance. This one is small enough that you can see how the lanes work from a drone photo. This only qualifies as a medium-large roundabout. We have them a whole lot bigger.*

If you start in the right-hand lane [up at the top of the pic] to turn right, then without crossing any lanes except in the initial entry phase [which is also helped by shorter white markings], then you are fed out to the correct exit.

Not all large roundabouts have this system. The ones that don't are far more hazardous to negotiate, even for one practised at the British structure.

From the OP's PennDoT link - this is how not to lane a roundabout.

There are too many areas of 'guesswork' if both lanes are used simultaneously. With this method you only need one idiot in the outside lane trying to turn left for it to quickly become chaos. [This is reminiscent of what I've seen in Spain, where half the drivers stay in the outside lane, no matter where their exit might be. You need eyes in the back of your head to negotiate one of those. It is one of those times where the 'bad' behaviour actually becomes safer, and so often you'll see everybody going round the outside, leaving the inside empty & effectively treating it as though it had no lanes & was just a single-track system.

In the UK a modern roundabout this small wouldn't be laned at all which makes everyone treat it as a single lane & follow rather than try to drive side-by side… mimicking the Spanish system, but officially. If it was laned, as older roundabouts tended to be, then it's a single dotted line right the way round, but with no other messages. That's why they're doing away with lanes on the smaller ones, it removes a lot of dangerous guesswork.

*Bigger roundabouts - I've never measured it but this one might be a mile round, under & over two motorways. We don't really do clover-leaf junctions so much in the UK. This one has great laning right round, except for one exit which makes it a nightmare. [On the right in this pic, but the pic is of an earlier laning structure, since replaced & easier to see] btw, they must have taken this photo at 8am on a Sunday, it's never this quiet ;)

The safety advantage of a roundabout is that it almost completely eliminates the possibility of a head-on collision. Almost. — Criggie, Sep 11 '22 at 19:45
If you are going to show pictures of mad roundabouts, how can you leave out [swindon](https://www.decisionmarketing.co.uk/wp-content/uploads/2013/08/rondoq.jpg)? — User65535, Sep 12 '22 at 11:54
Aside from the fact I was in danger already of being too anecdotal, I had thought to include [Hemel](https://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempstead)) [which is the only 6-er, the others all seem to just have 5 'satellites'], but decided against it. I went round the one at Denham only this morning, going to & from Pinewood ;) — Tetsujin, Sep 12 '22 at 12:04

score 4 · Answer 5 · answered Sep 19 '22 at 21:50

First, make sure you're talking about the same form of intersection. The safest form is called a Modern Roundabout, which was developed in the UK in the 60's. This form was first constructed in the US in 1990.

Large diameter traffic circles and rotaries are not built anymore because the large diameters enable speeds that are unsafe and cause congestion.

Many people confuse other and older styles of circular intersections with modern roundabouts. High speed, east coast rotaries, large multi-lane traffic circles (Arc D’Triomphe, Dupont Circle), and small neighborhood traffic circles are not modern roundabouts and UK 'roundabouts' are not the same as North American 'modern roundabouts'. The Brits even call a merry-go-round a kid’s roundabout.

What is, and is not, a modern roundabout: FHWA: https://safety.fhwa.dot.gov/intersection/roundabouts/ UMass video: https://www.umass.edu/newsoffice/article/new-umass-transportation-center-video WA DOT: http://www.youtube.com/watch?v=vsCoI7lERGE

The magic roundabout in Swindon, UK, is a form of Ring Junction.

Modern roundabouts are the safest form of intersection in the world - the intersection type with the lowest risk of fatal or serious injury crashes - (much more so than comparable signals). Modern roundabouts require a change in speed and alter the geometry of one of the most dangerous parts of the system - intersections. The reduction in speed to about 20 mph and sideswipe geometry mean that, when a crash does happen at a modern roundabout, you might need a tow truck, but rarely an ambulance. Visit the Insurance Institute for Highway Safety or FHWA for modern roundabout FAQs and safety facts.

Modern Roundabouts are proven safer than signals (FHWA): https://safety.fhwa.dot.gov/provencountermeasures/roundabouts/ https://safety.fhwa.dot.gov/intersection/innovative/roundabouts/

A Review of Evidence-Based Traffic Engineering Measures Designed to Reduce Pedestrian–Motor Vehicle Crashes: https://ajph.aphapublications.org/doi/full/10.2105/AJPH.93.9.1456

Freakonomics story: https://freakonomics.com/podcast/roundabouts/

Since their introduction to the US in 1990, with over 8,000 modern roundabouts in place, there have only been about 190 total reported fatal crashes at modern roundabouts. Compare that to over 30,000 annual roadway deaths in the US and about 8,000 fatal crashes per year at intersections. https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/810682

Regarding 'safety' I would advocate for only considering crashes that cause injury, and exclude property damage only crashes, however many statistics used for comparisons count all reported crashes, so you need to assume unreported crashes at different forms of intersection are comparable. In the US, what is required to be reported varies from state to state, only state-based comparisons may get closest to an accurate answer. Injury and fatal crashes are more likely to be reported, and required to be reported.

Are roundabouts actually statistically safer than traditional traffic patterns?

5 Answers5