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Author Topic: Crash prone 'modern roundabouts'  (Read 294373 times)

jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1925 on: October 02, 2018, 12:46:24 PM »

The Pennsylvania Department of Transportation reviewed data for 11 roundabouts on state routes at intersections that were previously stop or signal controlled.  The results looked very good:

•   Fatalities were reduced by 100 percent (from two to zero);
•   Serious injuries were reduced by 100 percent (from seven to zero);
•   Minor injuries were reduced by 95 percent (from 19 to one);
•   Possible/unknown severity injuries were reduced by 92 percent (from 49 to four);
•   Crashes causing only property damage decreased by 2 percent (from 49 to 48); and
•   The total number of crashes dropped 47 percent (from 101 to 54).

PennDOT Data Shows Pennsylvania Roundabouts Reducing Crashes, Injuries and Fatalities
https://www.penndot.gov/pages/all-news-details.aspx?newsid=536

The problem with the study is of the 11 roundabouts analyzed, all were simple single-lane roundabouts.  The fact is Pennsylvania hasn’t built many multi-lane roundabouts.  I just hope the state doesn’t fool themselves into thinking “multi-lane” roundabouts will see similar crash reductions based on the results of 11 single-lane roundabouts.  The state just recently constructed one of the first multi-lane roundabout in Pennsylvania on State 222 and… surprise, surprise… it’s seeing a lot more crashes than they expected.  Of course, the State 222 multi-lane roundabout wasn’t included in their study since it just opened this year.  But based on the great results of the “single-lane” roundabout study, officials have downplayed the increases in crashes on State 222, stating that “accidents will wane as people learn to navigate the new circle”.  I just feel like we have been here before… Pennsylvania should look closely at states like Michigan and Wisconsin if they want to see how large complex multi-lane roundabouts fair.  Here is a statement from PennDOT Secretary Leslie S. Richards:

"Our data shows that modern-day roundabouts reduce crash severity and injuries while improving traffic flow,"

No Leslie, your data shows that single-lane modern-day roundabouts reduce crash severity and injuries while improving traffic flow. It tells us nothing about how multi-lane roundabouts will perform in your state. PennDOT, don't start building complex multi-lane roundabouts willy-nilly based on the results of your little "single-lane" roundabout study. 

Once again, in defence of the agency, how many other traffic control devices have remarkable safety records when only being one lane each direction, but totally fall apart when adding a second lane in each direction? Virtually all types of traffic control work regardless of the number of lanes (though four-way stops with a lot of lanes can break down pretty quickly). Generally, the deciding factor in safety is the overall control: stop, yield, signal etc. Geometry also plays a role, but I guess it's not entirely obvious that the geometry of a multi lane roundabout really screws things up.
« Last Edit: October 02, 2018, 12:50:13 PM by jakeroot »
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tradephoric

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Re: Crash prone 'modern roundabouts'
« Reply #1926 on: October 02, 2018, 01:12:47 PM »

Time and time again the crash rates of multi-lane roundabouts (specifically 2x2 multi-lane roundabouts) are abnormally high.  You start to wonder if multi-lane roundabouts are the best choice when they have average crash rates of 4.0 MEV compared to a typical signalized intersection which only averages about 0.8 MEV.  Like i have said, when you have 4x more crashes at a roundabout there's no guarantee there is going to be a drop in injury crashes.  All i know is for the next decade we will hear how safe roundabouts are in Pennsylvania based on PennDot's "single-lane roundabout study"... even when they are proposing to build a complex 3x2 monstrosity.
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kphoger

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Re: Crash prone 'modern roundabouts'
« Reply #1927 on: October 02, 2018, 02:36:16 PM »

Back to the party a little late.....




Here's an aerial of the Van Dyke and 18 1/2 Mile with a proposed redesign. 



Having a straight shot exiting the roundabout could simplify the roundabout operation IMO.  Drivers circulating the roundabout who drive over a "straight only" arrow pavement marking would actually continue to drive "straight" as oppose to weave through the roundabout.  The green path in the picture is simply easier to drive than the blue path.   Notice that the blue path hugs the inside of the roundabout for much longer than the green path, so a driver who wishes to enter the roundabout doesn't know the circulating drivers intention till much later on.  With the blue path it's a guessing game if the vehicle is about to exit the roundabout or continue circulating through it.  Makes it much more likely a driver pulls out infront of someone because they "guessed" wrong.

Ten or twenty years ago, I was seeing design guides out there on the internet saying the approach to a roundabout should be curved (to "force" slowing) but the departure should be straight.  And that's exactly what you have pictured.  But I believe the change in mindset is as was mentioned earlier:  a straight-shot departure means more trouble for pedestrians crossing nearby.



A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.



Because I haven't been involved in such an accident after witnessing a few happen right in front of me due to this very movement. It's not rocket science to use a roundabout, but unfortunately it is to many motorists I encounter on my daily commute.

If you're assuming I'm full of shit why would I lie about something as trivial as knowledge of roundabout movements on an internet forum  :hmmm:
Why, there is no lies. I am treating this as an honest mistake on your side. Fact that you didn't get into an accident doesn't tell you know the drill - it may also be your luck and skill of people around you..
But back to technical matters:
Exit from inner lanes is an essencial design feature of roundabouts.
Old facioned circles can be different, though. Still the circle we're talking about, while not a "modern roundabout", but it is clearly setup to allow exit from left lane on 2 out of 5 legs.
A such, I would take your complain for "exit from no-exit lane", or "exit from left lane where that is not allowed" - but a plain "exit from left lane", combined with confusion between traffic circle and roundabout (later is a special case of a circle in common terminology) raises some red flags.

Indeed, if traffic were not allowed to exit from the inner lane of a roundabout, then why would there even be an inner lane?  If nobody were allowed to exit from it, then any driver foolish enough to end up there would just have to drive round and round in circles all day.



Minnesota truck drivers reveal their thoughts about the notorious roundabouts in Worthington, which has been the site of at least four confirmed truck tip-overs over the past year (all of which have been documented in this thread).  It just doesn't seem roundabout designers consider all the factors that truck drivers must deal with:

Risky roundabouts? Area truck drivers share thoughts about circular junctions
https://www.dglobe.com/news/traffic-and-construction/4494568-risky-roundabouts-area-truck-drivers-share-thoughts-about
Quote
“You’re top heavy, so you hit that impact curb and it tips the truck,” Schutte said.

Add in heavy winds, and these combined factors could easily cause the trailer to roll over, said Gary Abels, a Brewster semi driver and owner of Abels Transport. In addition to tipping, the truck apron can cause hang-up issues if the trailer has low ground clearance.

“My trailer is only four inches off the ground when it’s heavy, so then I have to avoid the apron,” Abels said.

On one occasion, Abels was forced to avoid Worthington roundabouts entirely. Delivering a planter to Worthington Ag Parts, he was not allowed to travel through the roundabout due to an oversized load, per state law.

“That’s another issue,” Abels said. “Trucks with oversized trailers can make normal turns, but they can’t go through roundabouts, so how are we supposed to get into town if they build even more roundabouts?”

Worthington is in the middle of huge agriculture.  When I was up there about a year ago, it was unbelievable how many trains and trucks were being filled up with corn and soybeans.  Heavy-laden trucks with inexperienced drivers behind the wheel is, frankly, the reality of life in farm country.  I know this because I grew up in farm country.  The Worthington roundabouts are also right on the primary route from the Twin Cities to Sioux City and the #2 route from the Twin Cities to Omaha.  Failing to account for heavy and/or oversize truck loads on that corridor is inexcusable.
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1928 on: October 02, 2018, 09:57:29 PM »

A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.

I think any intersection with fatalities is fatality-prone, at least retrospectively. His argument isn't that signals are safer. It's that multi-lane roundabouts aren't necessarily better.
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ScottRAB

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Re: Crash prone 'modern roundabouts'
« Reply #1929 on: October 04, 2018, 04:12:58 PM »

Total crashes at any intersection, regardless of traffic control, are not particularly relevant. 

People using the road make mistakes (like running stop signs and red lights), always have and always will. Crashes will always be with us, but they need not result in fatalities or serious injury.

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 usually need a tow truck, not an ambulance.  Visit the Insurance Institute for Highway Safety for modern roundabout FAQs and safety facts.  Roundabouts are one of several proven road safety features (FHWA). 
The life saved may be your own.
https://safety.fhwa.dot.gov/provencountermeasures/roundabouts/
https://safety.fhwa.dot.gov/intersection/innovative/roundabouts/
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1930 on: October 04, 2018, 04:27:07 PM »

^^
You should probably read the thread. Tradephoric and the rest of us have very carefully dissected the data behind roundabouts; it's not that cut and dry.

Consider this: the only thing forcing a driver to turn left or right is the steering wheel, not the geography surrounding the car.
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tradephoric

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Re: Crash prone 'modern roundabouts'
« Reply #1931 on: October 04, 2018, 04:43:08 PM »

The reduction in speed to about 20 mph and sideswipe geometry mean that, when a crash does happen at a modern roundabout, you usually need a tow truck, not an ambulance.  Visit the Insurance Institute for Highway Safety for modern roundabout FAQs and safety facts. 

These "20 mph" roundabout crashes look so safe... 




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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1932 on: October 04, 2018, 05:46:44 PM »


Hey, this one's cheating. The roundabout is still another 5 metres away.
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1933 on: October 04, 2018, 09:39:14 PM »

I'm not sure if it's been mentioned or not, but in Carmel, the 116th/Hazel Dell Pkwy signal has been reconfigured into this behemoth. We have a solid object in the middle, just in case someone forgets to turn their wheel on approach, and a third lane going southbound, for no obvious reason (2 lanes before and after, and northbound is only two lanes).

A simpler design with a flat center (with some bushes) might be prove safer long term, if tradephoric's data is to be believed.

The double right turn yield is pretty cool, though!

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kalvado

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Re: Crash prone 'modern roundabouts'
« Reply #1934 on: October 04, 2018, 09:57:24 PM »


Hey, this one's cheating. The roundabout is still another 5 metres away.
I would include approach geometry into roundabout statistics.
Same as rear ends (e.g. at red light cameras) are assigned to an intersection while they are still way outside the intersection box.
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1935 on: October 04, 2018, 10:54:58 PM »

https://www.youtube.com/watch?v=dYtmnzwJ4Cw

Hey, this one's cheating. The roundabout is still another 5 metres away.

I would include approach geometry into roundabout statistics.
Same as rear ends (e.g. at red light cameras) are assigned to an intersection while they are still way outside the intersection box.

Actually, I agree. I was being sarcastic but forgot to include the obligatory "/s".
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kphoger

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Re: Crash prone 'modern roundabouts'
« Reply #1936 on: October 05, 2018, 12:55:22 PM »

A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.

I think any intersection with fatalities is fatality-prone, at least retrospectively. His argument isn't that signals are safer. It's that multi-lane roundabouts aren't necessarily better.

I drove to my parents' house yesterday evening, 7 miles away, and then back again 1½ hours later.  I saw one wreck in each direction; one was at a business entrance crossing, and the other was at a stoplight.  The former was so severe that they were still cleaning up the scene 1½ hours later on my return trip.  So now both that stoplight and that business entrance crossing automatically become "crash prone"?

¼ mile in another direction from my house, there's another stoplight where I've seen two wrecks within a year's span.  Nothing weird about the intersection, just four-lane roads in each direction and a three-section signal.  But it must somehow be "crash prone".
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kalvado

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Re: Crash prone 'modern roundabouts'
« Reply #1937 on: October 05, 2018, 03:03:07 PM »

A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.

I think any intersection with fatalities is fatality-prone, at least retrospectively. His argument isn't that signals are safer. It's that multi-lane roundabouts aren't necessarily better.

I drove to my parents' house yesterday evening, 7 miles away, and then back again 1½ hours later.  I saw one wreck in each direction; one was at a business entrance crossing, and the other was at a stoplight.  The former was so severe that they were still cleaning up the scene 1½ hours later on my return trip.  So now both that stoplight and that business entrance crossing automatically become "crash prone"?

¼ mile in another direction from my house, there's another stoplight where I've seen two wrecks within a year's span.  Nothing weird about the intersection, just four-lane roads in each direction and a three-section signal.  But it must somehow be "crash prone".
You may divide any road areas into two groups: ones where fatal accident already occurred and those where it didn' happen yet.
However any serious crash, or repeat crashes, does require investigation of whether it is statistical fluctuation or a road issue. In the ideal world, at least. As a rule of thumb nobody cares until there is a fatality anyway.
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1938 on: October 05, 2018, 03:05:41 PM »

A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.

I think any intersection with fatalities is fatality-prone, at least retrospectively. His argument isn't that signals are safer. It's that multi-lane roundabouts aren't necessarily better.

I drove to my parents' house yesterday evening, 7 miles away, and then back again 1½ hours later.  I saw one wreck in each direction; one was at a business entrance crossing, and the other was at a stoplight.  The former was so severe that they were still cleaning up the scene 1½ hours later on my return trip.  So now both that stoplight and that business entrance crossing automatically become "crash prone"?

¼ mile in another direction from my house, there's another stoplight where I've seen two wrecks within a year's span.  Nothing weird about the intersection, just four-lane roads in each direction and a three-section signal.  But it must somehow be "crash prone".

Technically, every intersections is "crash prone"; what matters is how crash prone they are. Though, various agencies around the country (and the FHWA) would like you to believe that roundabouts, of any size or variety, are relatively less prone. And that does seem to be true at single-lane roundabouts, but at multi-lane roundabouts, they appear to be far more crash prone.
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jeffandnicole

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Re: Crash prone 'modern roundabouts'
« Reply #1939 on: October 05, 2018, 03:45:39 PM »

A single fatal crash is a significant event.  According to published data, signalized intersections in America average a fatal crash about every 100 years and drivers have only been driving through modern roundabouts in this country for 27 years.    Considering there have been 2 fatal crashes at Summerlin Nevada roundabouts over the past several months - the first community in America to build modern roundabouts – they instantly become fatality prone intersections.

If Wichita Falls, TX (a city with approximately the same population as Summerlin), were to have 2 fatal crashes at signalized intersections over the past several months, then would those instantly become fatality-prone intersections in your estimation?  If not, then you're applying a double standard.

I think any intersection with fatalities is fatality-prone, at least retrospectively. His argument isn't that signals are safer. It's that multi-lane roundabouts aren't necessarily better.

I drove to my parents' house yesterday evening, 7 miles away, and then back again 1½ hours later.  I saw one wreck in each direction; one was at a business entrance crossing, and the other was at a stoplight.  The former was so severe that they were still cleaning up the scene 1½ hours later on my return trip.  So now both that stoplight and that business entrance crossing automatically become "crash prone"?

¼ mile in another direction from my house, there's another stoplight where I've seen two wrecks within a year's span.  Nothing weird about the intersection, just four-lane roads in each direction and a three-section signal.  But it must somehow be "crash prone".

If a tree cutter fell a tree, and it happened to fall the wrong way on a car at an intersection killing someone inside, does that make the intersection crash prone?

Trade's never really been interested in reasoning behind something...he just looks at very basic info.  Fatal at intersection = crash prone.
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Re: Crash prone 'modern roundabouts'
« Reply #1940 on: October 05, 2018, 04:04:26 PM »

High speed, driver feel asleep, drink driver, truck with no brakes.... What a joke! That's an argument against 'something' but it has f#@$ all to do with roundabouts.

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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1941 on: October 05, 2018, 04:21:27 PM »

High speed, driver feel asleep, drink driver, truck with no brakes.... What a joke! That's an argument against 'something' but it has f#@$ all to do with roundabouts.

But they all hit something related to the design of the roundabout. Either a sign leading up to it, or the central island.

Would some of them have eventually crashed? Perhaps, but roundabouts create geographical hazards, which make them hard to navigate if you didn't notice them.

You can run a signal. You can't run a roundabout.
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billpa

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Re: Crash prone 'modern roundabouts'
« Reply #1942 on: October 05, 2018, 05:02:25 PM »

High speed, driver feel asleep, drink driver, truck with no brakes.... What a joke! That's an argument against 'something' but it has f#@$ all to do with roundabouts.

But they all hit something related to the design of the roundabout. Either a sign leading up to it, or the central island.

Would some of them have eventually crashed? Perhaps, but roundabouts create geographical hazards, which make them hard to navigate if you didn't notice them.

You can run a signal. You can't run a roundabout.
Please. A truck with no brakes? When are you guys going to start a "crash prone curves" topic. It won't be the dangerous truck, it'll be the curve that was in its way, a poor design.  This thread has become farce.

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Re: Crash prone 'modern roundabouts'
« Reply #1943 on: October 05, 2018, 05:05:02 PM »

High speed, driver feel asleep, drink driver, truck with no brakes.... What a joke! That's an argument against 'something' but it has f#@$ all to do with roundabouts.

But they all hit something related to the design of the roundabout. Either a sign leading up to it, or the central island.

Would some of them have eventually crashed? Perhaps, but roundabouts create geographical hazards, which make them hard to navigate if you didn't notice them.

You can run a signal. You can't run a roundabout.

Based on the opinions of some in this thread, roundabouts need to be made idiot-proof, just because there's a good chance a law-breaker will be able to screw-up at a traffic light and make it through unscathed. What next, do we need to make electric fences that don't shock someone if they decide to pee on it? Lawyers and politicians are killing our society and whatever is left of "common sense".
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jakeroot

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Re: Crash prone 'modern roundabouts'
« Reply #1944 on: October 05, 2018, 06:26:07 PM »

High speed, driver feel asleep, drink driver, truck with no brakes.... What a joke! That's an argument against 'something' but it has f#@$ all to do with roundabouts.

But they all hit something related to the design of the roundabout. Either a sign leading up to it, or the central island.

Would some of them have eventually crashed? Perhaps, but roundabouts create geographical hazards, which make them hard to navigate if you didn't notice them.

You can run a signal. You can't run a roundabout.

Based on the opinions of some in this thread, roundabouts need to be made idiot-proof, just because there's a good chance a law-breaker will be able to screw-up at a traffic light and make it through unscathed. What next, do we need to make electric fences that don't shock someone if they decide to pee on it? Lawyers and politicians are killing our society and whatever is left of "common sense".

As long as speeding, driving drunk, and inattentiveness aren't punishable by death, we should be trying to design for everyone, even morons. I fucking hate it. I'd rather we designed roads for only those with the intelligence to know how to properly operate vehicles, but that's not good PR. The best thing we can do? Make it a bit harder to get a licence. In the mean time, we can't seem to handle multi-lane roundabouts, or roundabouts with large objects in the middle.
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Re: Crash prone 'modern roundabouts'
« Reply #1945 on: October 05, 2018, 07:07:27 PM »

\
As long as speeding, driving drunk, and inattentiveness aren't punishable by death, we should be trying to design for everyone, even morons. I fucking hate it. I'd rather we designed roads for only those with the intelligence to know how to properly operate vehicles, but that's not good PR. The best thing we can do? Make it a bit harder to get a licence. In the mean time, we can't seem to handle multi-lane roundabouts, or roundabouts with large objects in the middle.
And then someday it happens to you. You are not feeling well, didn't sleep last night, quarreled with your significant other... You make a small tiny little mistake. And now rescue has to cut you out of a wreck. And at the hospital doctor looks skeptical. ANd nurse doesn't look into your eyes....
And you think - if only that curve was a bit more sha.... and then the darkness falls on you.
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Re: Crash prone 'modern roundabouts'
« Reply #1946 on: October 06, 2018, 11:13:20 AM »

I'm not sure if it's been mentioned or not, but in Carmel, the 116th/Hazel Dell Pkwy signal has been reconfigured into this behemoth. We have a solid object in the middle, just in case someone forgets to turn their wheel on approach, and a third lane going southbound, for no obvious reason (2 lanes before and after, and northbound is only two lanes).

A simpler design with a flat center (with some bushes) might be prove safer long term, if tradephoric's data is to be believed.

The double right turn yield is pretty cool, though!



The third lane going southbound helps with traffic volume during the morning rush hour.   The physical separation of the third lane by a median helps keep people in the appropriate lane.    This roundabout works very well to keep traffic moving.
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tradephoric

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Re: Crash prone 'modern roundabouts'
« Reply #1947 on: October 06, 2018, 11:38:47 AM »

Based on the opinions of some in this thread, roundabouts need to be made idiot-proof, just because there's a good chance a law-breaker will be able to screw-up at a traffic light and make it through unscathed. What next, do we need to make electric fences that don't shock someone if they decide to pee on it? Lawyers and politicians are killing our society and whatever is left of "common sense".

I think it's reasonable to design roundabouts with the assumption that a vehicle, at some point in the roundabouts useful life, will plow through the central island at high speed.  Sure, it may be a rare event, but when someone flies through the middle of a roundabout at high speed do we want a retaining wall built in the central island to become a near certain death warrant?  And you can't argue that it's a money issue.  Unlike a runaway truck ramp that adds more money to the design of a freeway, designing a roundabout that's void of fixed objects in the central island would be less expensive than adding a retaining wall or massive palm trees or some ornate statue to the central island.
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kalvado

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Re: Crash prone 'modern roundabouts'
« Reply #1948 on: October 06, 2018, 11:47:01 AM »

Based on the opinions of some in this thread, roundabouts need to be made idiot-proof, just because there's a good chance a law-breaker will be able to screw-up at a traffic light and make it through unscathed. What next, do we need to make electric fences that don't shock someone if they decide to pee on it? Lawyers and politicians are killing our society and whatever is left of "common sense".

I think it's reasonable to design roundabouts with the assumption that a vehicle, at some point in the roundabouts useful life, will plow through the central island at high speed.  Sure, it may be a rare event, but when someone flies through the middle of a roundabout at high speed do we want a retaining wall built in the central island to become a near certain death warrant?  And you can't argue that it's a money issue.  Unlike a runaway truck ramp that adds more money to the design of a freeway, designing a roundabout that's void of fixed objects in the central island would be less expensive than adding a retaining wall or massive palm trees or some ornate statue to the central island.
This is an interesting dilemma. You can design roundabout so that a car can fly through and possibly crash head-on or T-bone on the other side - or catch it in the center, even at a cost to a runaway vehicle. Non-injuring catcher is the best of both worlds, but I am not sure how to achieve that in a footprint of tiny circles squeezed into urban surroundings.
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Re: Crash prone 'modern roundabouts'
« Reply #1949 on: October 06, 2018, 12:18:50 PM »

I'm not sure if it's been mentioned or not, but in Carmel, the 116th/Hazel Dell Pkwy signal has been reconfigured into this behemoth. We have a solid object in the middle, just in case someone forgets to turn their wheel on approach, and a third lane going southbound, for no obvious reason (2 lanes before and after, and northbound is only two lanes).

A simpler design with a flat center (with some bushes) might be prove safer long term, if tradephoric's data is to be believed.

The double right turn yield is pretty cool, though!

https://www.dronegenuity.com/wp-content/uploads/2018/03/carmel-IN-roundabout-10.jpg

The third lane going southbound helps with traffic volume during the morning rush hour.   The physical separation of the third lane by a median helps keep people in the appropriate lane.    This roundabout works very well to keep traffic moving.

I think I get it now. There's so much traffic coming from the east, there has to be a triple lane entrance going south, because there are less gaps. Going north, there isn't as much traffic coming from the west, so traffic is able to enter more often without stopping.

Does that line up with your experience?
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