Crash prone 'modern roundabouts'

[DaBigE]

can easily be a cause for a crash if driver doesn't see it in advance.

That can be said for most any collision, whether a roundabout is involved or not: debris in the road, lane closure due to construction, a bridge abutment, or a building at the end of a T-intersection. Most roundabouts, especially those on higher-speed facilities don't just pop up out of nowhere. And if the driver misses all the cues, whether is numerous signs or via GPS, the type of intersection isn't going to matter. At least the curbing of a roundabout provides a better chance of the crash only involving a single vehicle, at a lower speed, and at an indirect angle, versus full-speed at a blunt angle.

The mentioning of fog wasn't intended to be in support of a roundabout vs. a signalized intersection, rather it was to emphasize how silly Trade's slippery-slope/what-if arguments are. That said, the roundabout at least has the potential for redirecting the vehicles into deviating paths, rather than all to a single point.

Showing a vehicle "threading the needle" while running a red light is just proving one thing: luck. Showing a drunken driver vaulting over a roundabout is all about location...a more serious crash could have occurred had that same drunk driver plowed through a traffic signal or a DDI, or smack into a bridge pier.

[kalvado]

can easily be a cause for a crash if driver doesn't see it in advance.

That can be said for most any collision, whether a roundabout is involved or not: debris in the road, lane closure due to construction, a bridge abutment, or a building at the end of a T-intersection. Most roundabouts, especially those on higher-speed facilities don't just pop up out of nowhere. And if the driver misses all the cues, whether is numerous signs or via GPS, the type of intersection isn't going to matter. At least the curbing of a roundabout provides a better chance of the crash only involving a single vehicle, at a lower speed, and at an indirect angle, versus full-speed at a blunt angle.

The mentioning of fog wasn't intended to be in support of a roundabout vs. a signalized intersection, rather it was to emphasize how silly Trade's slippery-slope/what-if arguments are. That said, the roundabout at least has the potential for redirecting the vehicles into deviating paths, rather than all to a single point.

Showing a vehicle "threading the needle" while running a red light is just proving one thing: luck. Showing a drunken driver vaulting over a roundabout is all about location...a more serious crash could have occurred had that same drunk driver plowed through a traffic signal or a DDI, or smack into a bridge pier.

OK, we're closer in opinions 
And "threading the needle" is about traffic volume after all. Randomly shooting through an intersection handling 50 thousand cars a day... I've seen bicyclist doing that - and that bastard lived to try that again! For 1000 cars a day - that is a much better chance than playing russian roulette.

One thing I would argue regarding roundabouts on a long stretch of a highway - driver can expect  minimal maneuvering knowing it is 100 rural miles along state rt. XXX - an expectation made unreasonable by roundabout  (but, to be fair, also by deer, broken car or farmer's tractor relocating to a different field)

[tradephoric]

Showing a vehicle "threading the needle" while running a red light is just proving one thing: luck. Showing a drunken driver vaulting over a roundabout is all about location...a more serious crash could have occurred had that same drunk driver plowed through a traffic signal or a DDI, or smack into a bridge pier.

In the future, connected vehicles will make it increasingly difficult to get t-boned by red-light runners.  At that point, it has less to do about "luck", and more to do with technology.  I'm not saying connected vehicles will stop every potential crash, but if new car tech can drastically reduce t-bone crashes at intersections then what becomes the safety benefit of roundabouts?    It becomes a big dumb circle in the middle of the road that is potentially hazardous to anyone approaching it too fast (this is your captain speaking... prepare for takeoff).  Considering connected vehicles is already a standard option on some vehicles on the road today, it's likely that widespread adaptation is coming.  Do you really think roundabouts are going to be hailed for their safety benefits in 20 years?

[DaBigE]

In the future, connected vehicles will make it increasingly difficult to get t-boned by red-light runners.  At that point, it has less to do about "luck", and more to do with technology.  I'm not saying connected vehicles will stop every potential crash, but if new car tech can drastically reduce t-bone crashes at intersections then what becomes the safety benefit of roundabouts?    It becomes a big dumb circle in the middle of the road that is potentially hazardous to anyone approaching it too fast (this is your captain speaking... prepare for takeoff).  Considering connected vehicles is already a standard option on some vehicles on the road today, it's likely that widespread adaptation is coming.  Do you really think roundabouts are going to be hailed for their safety benefits in 20 years?

I can't believe that you think CV technology will only have an impact on signalized intersections. (Your bias is peaking out once again.) One would also expect CV technology to make roundabouts safer and more efficient as well (think microsimulation models). "You're approaching this roundabout too fast, you must reduce your speed." Further, if vehicles were computer controlled, headways at roundabout could be tightened as they could be at traffic signals, thereby increasing the capacities from current calculations. Likewise, at some point, technology should make safety a moot point for all intersection control types. Technology could also render all intersection controls as we know them today useless...stop signs, yield signs, traffic signals, etc... as everything will be in-car.

Not all roundabouts are constructed for safety reasons. They have been proven to have higher capacity than other intersection controls, to a point, then they begin to break down. As for 20 years from now? WHO THE HELL KNOWS??? Twenty years ago, roundabouts were barely present in the US. At one point, it was thought we'd have flying cars by now...maybe we'll have them then. This whole discussion could be moot 2 years from now.

[jeffandnicole]

Showing a vehicle "threading the needle" while running a red light is just proving one thing: luck. Showing a drunken driver vaulting over a roundabout is all about location...a more serious crash could have occurred had that same drunk driver plowed through a traffic signal or a DDI, or smack into a bridge pier.

In the future, connected vehicles will make it increasingly difficult to get t-boned by red-light runners.  At that point, it has less to do about "luck", and more to do with technology.  I'm not saying connected vehicles will stop every potential crash, but if new car tech can drastically reduce t-bone crashes at intersections then what becomes the safety benefit of roundabouts?    It becomes a big dumb circle in the middle of the road that is potentially hazardous to anyone approaching it too fast (this is your captain speaking… prepare for takeoff).  Considering connected vehicles is already a standard option on some vehicles on the road today, it’s likely that widespread adaptation is coming.  Do you really think roundabouts are going to be hailed for their safety benefits in 20 years?

We won't need guardrails and signs and billions of dollars of other safety enhancements either.

[tradephoric]

Technology could also render all intersection controls as we know them today useless...stop signs, yield signs, traffic signals, etc... as everything will be in-car.

As for 20 years from now? WHO THE HELL KNOWS??? Twenty years ago, roundabouts were barely present in the US. At one point, it was thought we'd have flying cars by now...maybe we'll have them then. This whole discussion could be moot 2 years from now.

When I initially brought up connected vehicles you suggested that implementation by the consumer would be slow, pointing out that the average age of a car on the road is 11.5 years.  Now, just a few posts later, you are talking about flying cars and connected vehicles eliminating the need for traffic signals and stop signs.... and citing that this whole discussion could be moot "2 years from now" .   What happens in 2 years exactly?

[DaBigE]

Technology could also render all intersection controls as we know them today useless...stop signs, yield signs, traffic signals, etc... as everything will be in-car.

As for 20 years from now? WHO THE HELL KNOWS??? Twenty years ago, roundabouts were barely present in the US. At one point, it was thought we'd have flying cars by now...maybe we'll have them then. This whole discussion could be moot 2 years from now.

When I initially brought up connected vehicles you suggested that implementation by the consumer would be slow, pointing out that the average age of a car on the road is 11.5 years.  Now, just a few posts later, you are talking about flying cars and connected vehicles eliminating the need for traffic signals and stop signs.... and citing that this whole discussion could be moot "2 years from now" .   What happens in 2 years exactly?

I was responding directly to your latest post/question, and that one only, and you know that. Apparently you are the only one who can live in Hypothetical What-If Land. Grow up and cut the BS. It's not cute or funny any more (not that it ever was to begin with).

[tradephoric]

What if there's a bus full of little kids coming from all directions and all electronic devices fail, and they're in dense fog?

I legitimately responded to your hypothetical what-if land scenario.  Keeping it in context, I had just said that connected vehicles could dramatically reduce crashes at signalized intersections.  Seemingly you were suggesting that the buses full of little kids would get t-boned in the dense fog if the V2V fails (ie. all electronic devices fail).   I simply asked "if it's so foggy that the driver can't see the traffic signal, what makes you think they would be able to safely navigate through the sharp curves of a roundabout?"   In which you replied...

Headlights, streetlights, and street signs still work in fog. Throw in a power outage for good measure, and you still have headlights and retroreflective signs and pavement markings. No different than a car negotiating tight mountain pass curves.

Why would a driver approaching a traffic signal in dense fog have so much trouble seeing it, while a driver approaching a roundabout in dense fog could navigate through it just fine... like a car negotiating tight mountain pass curves as you put it?  You give this dense fog scenario, but the outcome changes whether the driver is approaching a traffic signal or a roundabout.  This is undeniable... if you take a roundabout too fast, it's a guaranteed crash.  When you blow through a red light you might get "lucky" as you put it and not get in a crash.... but in the future with connected vehicles, it won't be "luck" that the red-light runner didn't cause a crash.

[DaBigE]

What if there's a bus full of little kids coming from all directions and all electronic devices fail, and they're in dense fog?

I legitimately responded to your hypothetical what-if land scenario.  Keeping it in context, I had just said that connected vehicles could dramatically reduce crashes at signalized intersections.  Seemingly you were suggesting that the buses full of little kids would get t-boned in the dense fog if the V2V fails (ie. all electronic devices fail).   I simply asked "if it's so foggy that the driver can't see the traffic signal, what makes you think they would be able to safely navigate through the sharp curves of a roundabout?"   In which you replied...

Headlights, streetlights, and street signs still work in fog. Throw in a power outage for good measure, and you still have headlights and retroreflective signs and pavement markings. No different than a car negotiating tight mountain pass curves.

Why would a driver approaching a traffic signal in dense fog have so much trouble seeing it, while a driver approaching a roundabout in dense fog could navigate through it just fine... like a car negotiating tight mountain pass curves as you put it?  You give this dense fog scenario, but the outcome changes whether the driver is approaching a traffic signal or a roundabout.

Similar the mountain pass, a properly designed, higher-speed roundabout will have several more cues as the driver approaches: at least one warning sign, diagrammed guide sign(s), and transitional lighting, all of which spaced far enough away for the driver to react. Better designs also employ curbing along the approach, well before any curves begin, including the splitter island. Just of a lighting standpoint, higher-speed traffic signals rarely have transitional lighting, relying instead on lights at the actual intersection - too late for a driver to react if still at full speed. At a traffic signal, you're lucky if there's a Signal Ahead warning sign. Even if one is posted, it's a guessing game for the driver as to how far downstream the signal actually is...even worse if the signals are not working.

When you blow through a red light you might get "lucky" as you put it and not get in a crash.... but in the future with connected vehicles, it won't be "luck" that the red-light runner didn't cause a crash.

And as I eluded to earlier, in the future technologically-rich environment we all are waiting for, the driver will also be warned on approach to roundabout, and whether their speed is prudent, and how much conflicting traffic may be approaching from the left.

[tradephoric]

And as I eluded to earlier, in the future technologically-rich environment we all are waiting for, the driver will also be warned on approach to roundabout, and whether their speed is prudent, and how much conflicting traffic may be approaching from the left.

Really?  When the scenario was buses approaching a signalized intersection in dense-fog, you alluded to the V2V tech failing and NOT warning drivers of the approaching light.  Only when the drivers are approaching a roundabout do you suggest that the V2V technology would actually work.  Then you claim that my bias is peaking, when you are the one giving roundabouts every benefit of the doubt and assume the worst at signals.

[DaBigE]

And as I eluded to earlier, in the future technologically-rich environment we all are waiting for, the driver will also be warned on approach to roundabout, and whether their speed is prudent, and how much conflicting traffic may be approaching from the left.

Really?  When the scenario was buses approaching a signalized intersection in dense-fog, you alluded to the V2V tech failing and NOT warning drivers of the approaching light.  Only when the drivers are approaching a roundabout do you suggest that the V2V technology would actually work.  Then you claim that my bias is peaking, when you are the one giving roundabouts every benefit of the doubt and assume the worst at signals.

No where, did I say that (referring to the part in bold). You provided several what-if scenarios, so I did one as well. No electronic device is immune to faults and failures from time to time, so that's what I based my scenario on. No where did I ever suggest V2V would not help traffic signal operations. You're the one who keeps implying that traffic signals are the only places that will benefit from V2V technology. I'm trying to keep an open and objective mind to all intersection control options. You, OTOH, try to find every minute opportunity to slam the door on roundabouts. I said it before, but your selective memory/reading makes it apparent that I need to say it again:
Roundabouts are not a silver-bullet traffic solution (nor a faultless solution), but they are a viable option in many circumstances.

[jakeroot]

A new interchange along the 405 @ NE 85th St near Kirkland, WA is planned to be redeveloped from a cloverleaf into a multi-level roundabout interchange. The lower level multi-lane roundabout is to be for general purpose traffic, the middle level single-lane roundabout for buses and toll users, and the upper level for the 405 (no roundabout of course).

An additional roundabout is planned for Kirkland Way to the west.

https://seattletransitblog.com/2018/04/30/kirklands-ne-85th-brt-station/

[kphoger]

A new interchange along the 405 @ NE 85th St near Kirkland, WA is planned to be redeveloped from a cloverleaf into a multi-level roundabout interchange. The lower level multi-lane roundabout is to be for general purpose traffic, the middle level single-lane roundabout for buses and toll users, and the upper level for the 405 (no roundabout of course).

An additional roundabout is planned for Kirkland Way to the west.

https://seattletransitblog.com/2018/04/30/kirklands-ne-85th-brt-station/

Isn't this off-topic?  If it hasn't even been built yet, it's neither crash-prone nor...well, not crash-prone.

Well, I guess if tradephoric had posted the article, it would have been accompanied by something like, I wonder how many toddlers and puppy dogs will die a terrible and painful death.

[kalvado]

A new interchange along the 405 @ NE 85th St near Kirkland, WA is planned to be redeveloped from a cloverleaf into a multi-level roundabout interchange. The lower level multi-lane roundabout is to be for general purpose traffic, the middle level single-lane roundabout for buses and toll users, and the upper level for the 405 (no roundabout of course).

An additional roundabout is planned for Kirkland Way to the west.

https://seattletransitblog.com/2018/04/30/kirklands-ne-85th-brt-station/

Isn't this off-topic?  If it hasn't even been built yet, it's neither crash-prone nor...well, not crash-prone.

Well, I guess if tradephoric had posted the article, it would have been accompanied by something like, I wonder how many toddlers and puppy dogs will die a terrible and painful death.

It may be an interesting case to discuss. Roundabout highway interchange are topologically equal to good old diamond interchanges with some right-of-way tweaking added.
This is an entire new level of complexity with express/transit added into the sandwich. Cost of $300M is.... quite impressive, to say the least.
I don't know what are the traffic counts, bus passenger counts are relatively low according to the link.

So we may talk about:
-appropriate spending margins and who is getting kickbacks
-expected functionality of roundabouted diamond (and I suspect flyover ramps are not out of question given the cost)
-expected driver confusion level (looks like medium-raw cluster-k to me with those predominantly left exits, maybe I could get used to that after few weeks) and associated accident rate (whoa, finally back on topic!)

[tradephoric]

Well, I guess if tradephoric had posted the article, it would have been accompanied by something like, I wonder how many toddlers and puppy dogs will die a terrible and painful death.

Don't forget the little piggies!  Remember that roundabout in Worthington, Minnesota?  Not only have there been multiple truck rollovers at the roundabout, other vehicles have flown straight over it Dukes of Hazzard style. 

These little piggies almost didn't make it to market when a Minn. hog truck rolled[/b][/size]

http://www.agweek.com/news/4350581-these-little-piggies-almost-didnt-make-it-market-when-minn-hog-truck-rolled

[tradephoric]

This is an entire new level of complexity with express/transit added into the sandwich. Cost of $300M is.... quite impressive, to say the least.
I don't know what are the traffic counts, bus passenger counts are relatively low according to the link.

That cost is quite impressive.  With the likely overruns, it will equate to about $1 for every American citizen to build this thing.  Of course that's not that bad considering the debt per American citizen in this country is $64,632 (and debt per taxpayer is $174,408).

[kalvado]

This is an entire new level of complexity with express/transit added into the sandwich. Cost of $300M is.... quite impressive, to say the least.
I don't know what are the traffic counts, bus passenger counts are relatively low according to the link.

That cost is quite impressive.  With the likely overruns, it will equate to about $1 for every American citizen to build this thing.  Of course that's not that bad considering the debt per American citizen in this country is $64,632 (and debt per taxpayer is $174,408).

We are talking about Seattle, a rich city with city budget of $10k per resident. I would still call it a bit pricey one, but they have Boeing and Amazon, they can afford spending few extra (billion) bucks..

[kphoger]

Don't forget the little piggies!  Remember that roundabout in Worthington, Minnesota? 

Yep, I remember it.  The only roundabout where I've genuinely been worried the person next to me was going to bang into the side of my car.  Two consecutive roundabouts in Worthington, as a matter of fact.

[MNHighwayMan]

Don't forget the little piggies!  Remember that roundabout in Worthington, Minnesota? 

Yep, I remember it.  The only roundabout where I've genuinely been worried the person next to me was going to bang into the side of my car.  Two consecutive roundabouts in Worthington, as a matter of fact.

There's actually three roundabouts on MN-60 in Worthington, though I'm not sure you'd call them "consecutive," per se. And coincidentally, I drove through two of them on Saturday and didn't find anything out of the ordinary or "scary."

[kphoger]

Don't forget the little piggies!  Remember that roundabout in Worthington, Minnesota? 

Yep, I remember it.  The only roundabout where I've genuinely been worried the person next to me was going to bang into the side of my car.  Two consecutive roundabouts in Worthington, as a matter of fact.

There's actually three roundabouts on MN-60 in Worthington, though I'm not sure you'd call them "consecutive," per se. And coincidentally, I drove through two of them on Saturday and didn't find anything out of the ordinary or "scary."

Well, the menace was no longer next to me by the time I got to the third roundabout that day.  See below for my original account.

Worthington Minnesota roundabout

It was only due to my attentiveness that I didn't get side-swiped at two of Worthington's roundabouts last month.  In fact, the experience made me think of this thread at the time.  But, since they are 2x1 rather than full 2x2, I didn't bring it up.

The main road (MN-60) is striped as two lanes in each direction through the roundabouts.  The driver next to me didn't seem to be the most capable, and seemed like the kind who drives as if she's the only one on the road.  So I decided to lag behind just a little bit as we drove through–which was fortunate, because she took both lanes and would have run into me if I hadn't lagged behind.  At the next roundabout, it was the same thing.  Good thing for me, she was getting off the highway at that second roundabout–turning left, I might add, from the right entry lane.  I can understand trucks and buses taking two lanes through a roundabout, but pure disregard for other drivers is just really irritating to me.

[tradephoric]

By the way the pig slaughtering roundabouts aren't limited to America.  A lorry carrying 200 pigs overturned at a roundabout on the A68 near Darlington just hours ago. It injured the driver and killed several of the pigs.  Good thing the lorry didn't catch fire after it tipped over as it was reported the driver was trapped inside the vehicle.  That situation does sound "scary" to me.

Pigs killed after lorry carrying 200 animals overturns on roundabout
https://www.gazettelive.co.uk/news/teesside-news/pigs-killed-after-lorry-carrying-14626787

[kalvado]

By the way the pig slaughtering roundabouts aren't limited to America.  A lorry carrying 200 pigs overturned at a roundabout on the A68 near Darlington just hours ago. It injured the driver and killed several of the pigs.  Good thing the lorry didn't catch fire after it tipped over as it was reported the driver was trapped inside the vehicle.  That situation does sound "scary" to me.

Pigs killed after lorry carrying 200 animals overturns on roundabout
https://www.gazettelive.co.uk/news/teesside-news/pigs-killed-after-lorry-carrying-14626787

We need a new sign to be added to MUTCD..

[jakeroot]

I originally posted the story on the 405/Kirkland roundabouts because I thought it would piss tradephoric off. An interchange that could easily be reconfigured into a Parclo B4, instead becoming a three level roundabout?! Oh the horror. Also, it's another new dual lane roundabout, which this thread has become a dumping ground for.

This is an entire new level of complexity with express/transit added into the sandwich. Cost of $300M is.... quite impressive, to say the least.
I don't know what are the traffic counts, bus passenger counts are relatively low according to the link.

That cost is quite impressive.  With the likely overruns, it will equate to about $1 for every American citizen to build this thing.  Of course that's not that bad considering the debt per American citizen in this country is $64,632 (and debt per taxpayer is $174,408).

We are talking about Seattle, a rich city with city budget of $10k per resident. I would still call it a bit pricey one, but they have Boeing and Amazon, they can afford spending few extra (billion) bucks..

To be fair, the citizens in the Sound Transit taxing district are paying for the interchange, not just the local cities. The interchange is funded as part of ST3, a $50B+ taxing package to expand transit across the Seattle region. The BRT line along the 405 is part of that package.

[kphoger]

Also, it's another new dual lane roundabout, which this thread has become a dumping ground for.

My one takeaway from this whole thread is that there are problems inherent in full dual-lane roundabouts:  specifically that there are non-glancing conflict points.  And that statistics for both single-lane roundabouts (with no such non-glancing conflict points) and dual-lane roundabouts should not be combined, lest the results be misleading.

[kalvado]

Also, it's another new dual lane roundabout, which this thread has become a dumping ground for.

My one takeaway from this whole thread is that there are problems inherent in full dual-lane roundabouts:  specifically that there are non-glancing conflict points.  And that statistics for both single-lane roundabouts (with no such non-glancing conflict points) and dual-lane roundabouts should not be combined, lest the results be misleading.

If you will, I have a slightly wider version of this. What is the role of roundabouts in a grand scheme of things in terms of throughput? Where would you put roundabout in a list of intersection designs with increasing throughput - that is: 4-way stop, traffic light, grade separated?
I would say that roundabouts belong to busy 4-way stop/not-so-busy traffic light interval. We had some european guidelines here showing a 30K/daily limit for complex roundabout, which seems reasonable to slightly optimistic; and I know a (very busy) traffic light controlled intersection with 50k+ daily traffic.
Now you can increase traffic light throughput quite a bit by adding components, such as dedicated turn lanes or slip ramps - of course at a cost of footprint. And those upgrades can be fairly seamless, you don't have to bulldoze entire thing for an extra lane (although imminent domain of land is a pain..)
You can also upgrade stop signals to a traffic light.
Roundabout, however, is a solution with limited throughput which can NOT be easily upgraded to next tier - which is complex traffic light.
And that can easily become a problem: no upgrade short of increasing complexity beyond the reason OR total rebuild.... Or continue funneling traffic through intersection above design limit - and pretend problem doesn't exist.