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Safety benefits of roundabouts

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Re: Safety benefits of roundabouts

#61

Post by Arrath »

marginalia_nu wrote: post #60
Arrath wrote: post #42

Earlier quoted context omitted.

Please, the average driver has trouble enough merging into traffic.

Well, when you mention it, I do think it's possible to join these 3d roundabouts into a 4d roundabout, essentially putting them on the vertices of a tesseract, permitting drivers in 4 dimensional space to safely meet on the 3d-dimensional surface of a 4-dimensional hyper-sphere. Of course it's a real spaghetti intersection where you need to potentially navigate dozens of 2D roundabouts to get to any given direction.…

"And that, kids, is the story of how I T-boned myself."

Re: Safety benefits of roundabouts

#62

Post by marginalia_nu »

Arrath wrote: post #61
marginalia_nu wrote: post #60

Earlier quoted context omitted.

Well, when you mention it, I do think it's possible to join these 3d roundabouts into a 4d roundabout, essentially putting them on the vertices of a tesseract, permitting drivers in 4 dimensional space to safely meet on the 3d-dimensional surface of a 4-dimensional hyper-sphere. Of course it's a real spaghetti intersection where you need to potentially navigate dozens of 2D roundabouts to get to any given direction.…

"And that, kids, is the story of how I T-boned myself."

Now you're thinking with portals!

Re: Safety benefits of roundabouts

#63

Post by eesmith »

simondotau wrote: post #32
grecy wrote: post #7

I grew up in a town in Australia nicknamed "The City of Roundabouts". Essentially all intersections in the entire town are roundabouts, including two lane ones, etc. It's quite common to drive the entire length of town (~20 blocks) in reasonably heavy traffic without ever stopping. On a good day you do it in 2nd gear, the whole way. At night you can do it in 3rd gear, because it's exceptionally easy to see headlights…

In my two decades of driving I’ve seen one 4-way stop in Australia. The intersection of Dickson Avenue and Clarendon Street, Artarmon NSW. Haven’t seen one anywhere else.

Street View - https://www.google.com/maps/@-33.8160242,151.1838978,3a,75y,...

Apparently there was one in Rockingham, Western Australia, says https://www.news.com.au/technology/innovation/motoring/fourw... ("Four-way stop sign stumps WA motorists, brings traffic to a standstill") but it is not there now at https://www.google.com/maps/@-32.2753035,115.7324187,3a,75y,... .

Re: Safety benefits of roundabouts

#64

Post by smegsicle »

sokoloff wrote: post #21
squarefoot wrote: post #8

Safety aside, roundabouts lower traffic significantly by never forcing cars to stop. Congestion increases as cars need to stop because of the inevitable latency propagating along the tails, and having more than one traditional intersections along the way can only make things even worse, so any solution to prevent cars from slowing down to a stop would mitigate those effects.

Until you do what Cambridge, MA has done twice near my house: put a traffic light just outside the roundabout, so when the light turns red, traffic inevitably backs up through the roundabout, locking it up entirely. https://www.google.com/maps/@42.3875777,-71.1422076,18z?entr...

note that proper spinlock procedure is to not leave the roundabout unless there is room to do so completely

this avoids complete deadlock until the entire roundabout is full of drivers who refuse to take any unblocked exit, while continually offering each the ability to do so

Re: Safety benefits of roundabouts

#65

Post by throw0101a »

_zamorano_ wrote: post #53

In Spain we use roundabouts heavily. They're perfect for crossings with low to middle traffic. No useless waiting time, good visiblity and no need for traffic lights. For heavy traffic, though, they're useless as the car flow of one entry/exit can take over the roundabout and block all other entries. Also, it seems hard to understand for many drivers that regulations regarding changing lanes don't change in a roundab…

> For heavy traffic, though, they're useless as the car flow of one entry/exit can take over the roundabout and block all other entries.

Not wrong, but traffic lights can be added to roundabouts as well ("signalized roundabouts")

* https://www.youtube.com/watch?v=XCrAPcUzOdw

So if an intersection is (e.g.) four-way, and one particular entrance monopolizes things than it can be given red at times and the others green (and than one-green/three-reds).

See (e.g.) "Performance and Safety of Roundabouts with Traffic Signals" by Tracz and Chodura:

> The paper presents designs, advantages and some drawbacks of various layouts of roundabouts with traffic signals, used in urban arterials on crossings with large traffic volumes. The authors analyze signal settings with alternative phasing used at intersections that can provide the intersection capacity of about 6500 veh/h in 2x2 lanes arterials or even 8000 veh/h in 2x3 lanes arterials. Accident statistics for roundabouts with traffic signals in Krakow are also given and discussed. In addition, presented are practical examples of changes of signalized roundabouts geometry; reconstruction into a form of turbo- roundabout and its effects regarding traffic safety and good performance.

* https://pdf.sciencedirectassets.com/277811/1-s2.0-S187704281...

And §8.1 Traffic Signals at Roundabouts:

* https://www.fhwa.dot.gov/publications/research/safety/00067/...

Also:

* https://www.access-board.gov/research/prow/literature-rounda...

Re: Safety benefits of roundabouts

#66

Post by sokoloff »

smegsicle wrote: post #64
sokoloff wrote: post #21

Earlier quoted context omitted.

Until you do what Cambridge, MA has done twice near my house: put a traffic light just outside the roundabout, so when the light turns red, traffic inevitably backs up through the roundabout, locking it up entirely. https://www.google.com/maps/@42.3875777,-71.1422076,18z?entr...

note that proper spinlock procedure is to not leave the roundabout unless there is room to do so completely this avoids complete deadlock until the entire roundabout is full of drivers who refuse to take any unblocked exit, while continually offering each the ability to do so

> not leave the roundabout unless there is room to do so completely

I don't understand how that helps. The problem is there are too many cars in the rotary, so no amount of not leaving the rotary will unblock it. It seems like you should not enter unless there's room to exit, but on some of these, you can't both see the exiting traffic light and safely merge into moving rotary traffic, so I don't really blame drivers who enter the rotary and find the light turns amber then red on them.

Re: Safety benefits of roundabouts

#67

Post by giraffe_lady »

gniv wrote: post #36

Here in France they have both types of roundabouts, yield-to-left-on-entry and yield-to-right. They are well signaled, so there is no confusion. The latter type is less common and seems to be mostly in less-busy areas. I'm not sure why they still use them though. Is it because you have better visibility to the right, since you're already in the intersection? It's an interesting design choice.

I think the yield-to-right ones are primarily a traffic calming thing, where the threat to yield limits how fast you can comfortably go through them. They use a lot of yield-to-right intersections in residential areas with poor visibility for the same reason. It's conceptually similar to the 4-way stops on low-traffic streets in the US, just streamlined and formalized.

Re: Safety benefits of roundabouts

#68

Post by devnull3 »

Simple roundabouts are definitely good but in UK I have found spiral roundabouts error prone if you have not driven on it before Example: [1]

When visiting for the first time on a specific spiral roundabout:

1. Lane markings are faded

2. You do not know the specific lane unless you come very close to it and have to make a quick decision

3. Often due to queued traffic you cannot even see the lane marking until its too late.

Because of this I have seen people change lanes on a roundabout because they made a mistake and its dangerous.

[1] https://www.google.com/maps/place/Sainsbury's/@51.5080462,-0...

Re: Safety benefits of roundabouts

#69

Post by m463 »

SoftTalker wrote: post #51
hristov wrote: post #20

The greatest thing about roundabouts is that they protect against the idiot that goes through an intersection at full speed. He does that either because he is passed out behind the wheel or because he did not notice a stop sign and thought he had the right of way, or maybe because he just does not care. Well with a roundabout if you just go straight ahead you hit the center circle. Good roundabouts always have a slig…

I knew a guy who didn't stop at all-way stop signs. His thinking was: if everyone else is going to stop, why should I?

two of those guys would cancel out.

Re: Safety benefits of roundabouts

#70

Post by tpmx »

hristov wrote: post #20

The greatest thing about roundabouts is that they protect against the idiot that goes through an intersection at full speed. He does that either because he is passed out behind the wheel or because he did not notice a stop sign and thought he had the right of way, or maybe because he just does not care. Well with a roundabout if you just go straight ahead you hit the center circle. Good roundabouts always have a slig…

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