California debuts 'turbo roundabout' to fix intersection near Bay Area | Hacker News Reader

California debuts 'turbo roundabout' to fix intersection near Bay Area

sfgate.com

34 pointsvasco93 comments

Looking at the old intersection on the satellite map photos, it’s a classic obstructed-A-pillar deathtrap with traffic lights glued on as a failed band-aid fix.

See also Ipley Cross, which had the same issue until it was altered last year or so into two right-angle T-intersections separated by a few hundred feet: https://news.ycombinator.com/item?id=23024275 (4 years ago, 144 comments)

The DOT pages for the Gilroy project may be of interest:

https://dot.ca.gov/caltrans-near-me/district-5/district-5-cu...

http://sanbenitocog.org/wp-content/uploads/2023/10/Turbo-Rou... [pdf]

http://sanbenitocog.org/wp-content/uploads/2023/10/SR-156-Im... [pdf]

For those in other regions: US traffic signals generally permit a right turn at a stop/red signal after coming to a complete stop, do not use photo enforcement to detect red light violations, and are sometimes ignored by drivers when they don’t see any cross-traffic worth slowing down for. These three properties exacerbate the safety issues with scissor intersections and inhibit the effectiveness of signaling-only fixes.

1 and 2 can be addressed though.

It’s easy to ban right-turn-on-red on a specific intersection. People sometimes do not see the sign, but new-style electronic no-right-turn signs addresses this. https://www.orangetraffic.com/wp-content/uploads/2017/08/LS2...

It’s also legal to have red light cameras, so they can be installed.

American drivers disregard those electronic signals almost as readily as they disregard unlit signs, stop signs and red lights; especially in rural farmland regions such as Gilroy. (Less so when it’s due to a train track, more so when it’s due to impaired visibility.)

Red light cameras are a somewhat effective solution for attentive drivers, so long as their car has a license plate (which is also not reliably enforced in the US). However, the inherent flaws of the scissor intersection, and the risks posed by inattentive drivers, are only addressed by replacing the scissor intersection with something else.

> so long as their car has a license plate (which is also not reliably enforced in the US).

What? If any cop sees you without a plate you’re getting pulled over immediately.

I’ve seen two cars driving without plates within 5 miles of my house just this week.

Do you see police officers every single time you drive anywhere (or walk, bike, bus, whatever)? I know I don’t. And even if you do see one, they might have multiple reasons they’ll cite for why they didn’t stop X vehicle for Y infraction.

I also see at least one car without a plate every day I drive in my metropolitan area. Perhaps other areas are more rigorous. But certainly there’s also Portland (Oregon) or Berkeley (California), where the police no longer allow it:

https://www.oregonlive.com/crime/2021/06/portland-police-wil...

The only time I was stopped for a missing rear plate in my ~week of waiting for new car plates a couple years ago, was once by the state police. I imagine it’s because I had a new car and they were confused about how I ended up without plates, which was definitely an unusual scenario.

Thanks for these links, they are super informative! The split of the project with only ~10% of the project coming from state money, with federal money making up ~90% of the $15M, is quite interesting.

It's always fascinating how expensive car infrastructure is in comparison to, say, bike infrastructure. Additionally, it's interesting how there's approximately zero public process for these very expensive car infrastructure process, but a mere bike lane will ensure years of public input, each meeting a chance to veto the project but without any meetings that would allow the bike to definitively be built without further meetings.

Caltrans publishes a guide detailing how and when public input is consulted.

https://dot.ca.gov/-/media/dot-media/programs/transportation...

I encourage using the information within to contribute to local and regional planning processes. Note, however, that this does not address the environmental impact lawsuits often used by California drivers to obstruct bicycle infrastructure.

Thanks! I was going to link this after just seeing the article. Nice find on the corridor project too.

Oh boy, I can't imagine how much the local facebook groups would complain if a new different turbo roundabout were to be installed where I live.

Despite there now being at least a couple dozen roundabouts within 15 miles of here, every new installation generates a cacophony of kvetching. There have been roundabouts here for almost 2 decades now but people still treat them like the devil himself created them. Thankfully the number of people going the wrong way around the one near my home has diminished to almost none.

Back on topic, I like the design of this, it sort of sidesteps the lane changing that larger roundabouts use.

I live in the Bay Area but I grew up in the UK where we have lots of great roundabouts and I can tell you that the roundabouts in California are beyond terrible - why? Because pedestrians have right-of-way at the roundabout entry/exit points, so cars have to constantly stop on the roundabout, defeating its very purpose. Indeed, there's usually a marked crosswalk at every entry/exit (and even if not pedestrians have the right of way on "unmarked crosswalks" in CA).

In the UK roundabouts are the only place where pedestrians don't have right of way and there's always a small island in the center of each (unmarked) crosswalk, so only one direction of traffic needs to be crossed at a time. The cars flow around the roundabout and don't stop.

Are you sure about that? I'm not a UKian but the rules seem to imply that you have to give easy to pedestrians at roundabouts

You should come to Massachusetts. We up the ante by adding stoplights, stop signs, left turns, and pretty much any permutation of road topology.

You can avoid that issue by offsetting the pedestrian crossing one car's length from the roundabout. This allows a single car to stop and yield, while allowing subsequent cars going to other directions to continue unimpeded. It also reduces the angle between driver and pedestrian, greatly improving visibility. You can see this in practice at [0].

[0]: https://www.google.com/maps/@52.1124016,5.1914329,70m/data=!...

>This breaking news story has been updated.

lol yes, the months-long process of constructing a roundbaout definitely qualifies as "breaking news"

The DOT's video on using this roundabout is actually very clear and well made: https://m.youtube.com/watch?v=KHYo7Bl_zWg I'd say it does a better job than the linked article to explain how this roundabout is different from a usual roundabout and how the lanes work.

Since there's no picture in the article(!):

https://www.google.com/maps/place/CA-25,+California/@36.8954...

Oh! The road diagram includes the new roundabout but the satellite picture hasn't been updated!

36.89558° N, 121.42738° W

this article seems to have some actual pictures: https://metro.co.uk/2024/01/04/californians-will-get-used-us...

the previous configuration as shown on the satellite image looks a lot like the intersection Tom Scott made a video about, where the intersecting road is angled to keep cross-traffic hidden behind a car's a-pillar. https://www.youtube.com/watch?v=SYeeTvitvFU

Well, artist's renditions anyway.

Imagine designing an intersection between two roads with two lanes in either direction as a flat intersection. It's being lazy and cheap to the point of being criminal. Or it's almost like it wasn't really designed at all, it just sort of happened because two roads crossed. The way those roads are long and straight leading into the intersection too. Crazy. Any drunk/unattentive driver is going to go what 40-50mph against a red light right through that intersection. Good thing they removed it. Few hundred of those left to fix I'm sure. The road overlay shows the size of the roundabout really isn't much larger than the original intersection either.

Animation of a turbo roundabout: https://www.youtube.com/watch?v=AkmelZhvlPk (or search for 'turbo rotonde', there is a lot of material in Dutch available).

There are over 2000 of these turbo roundabouts in the Netherlands.

Or rather, 'turborotonde' if you want Dutch sources where it was spelled correctly.

They have been here in the Netherlands for decades so feels odd to see it is such a novelty in California. Happy to see they work there too!

In the city where I live, also in the Netherlands, we had multiple of these but all of them got converted back to normal intersections with traffic lights and it has been a huge improvement.

Can I ask where? I just moved to your country in late 2022 so I’m not sure what I would search for to read more.

My understaning is that normal intersection with traffic lights has higher troughput (as cars can just fly through it at or near 50 km/h if the green light is long enough), but roundabout have lower average wait times (if the traffic is low to moderate, you usually wait less that 5-10 seconds to enter the intersection).

No, simple roundabouts are worse in both throughput and wait times than normal intersections with traffic lights. They are however safer, and that safety is precisely thanks to slowing traffic town, which means that collisions are less frequent because drivers have more time to react and if a collision happens it happens at lower speed. Just think about it: how can wait time be smaller and throughput higher when cars approaching a roundabout from _any_ direction need to slow down compared to normal intersection where cars on one road can wizz through with full speed?

To answer your question: wait times can be lower because, if the traffic is low enough, ALL cars just wizz through, at the cost of slowing down while entering the roundabout. Whereas, for the intersection with traffic lights, a significant number of cars will hit red light and have to wait for a minute or two.

Except it's not true. You can't wizz through a roundabout because the road is curved, you are physically unable to drive through it with the same speed as you drive on a straight road. It's by design. When traffic is very light then the traffic lights can be simply disabled (for instance, at night). Not disabling them is the failure of the people responsible for the traffic lights, not some inherent unsolvable problem.

This depends on how light the traffic is. In a lot of places, traffic outside of rush hours is light to moderate (but definitely not light enough to justify disabling the lights), and the roundabouts might the more efficient solution, at least outside of rush hours. It was probably studied by someone already, as this would make a decent research topic for any transporation scientist.

In light traffic roundabouts are actually worse than normal intersection. How can it even be disputed? Let's say you have one car per hour, or any number of cars approaching in such a way that none of them gets close to the intersection at the same time. It goes through normal intersection without much slow down. It goes through equivalent roundabout _always_ slowing substantially down. What's here to dispute? If you have cars approaching at the same time then it gets a bit more complicated but the claim that in such a situation you can still always beat normal intersection is just ridiculous, because if the cars show up at exactly the right time some of them still need to completely stop before entering roundabout because there is already another car circling it. Analogously with normal intersection you don't need to always stop before entering it because both cars might be turning into perpendicular roads and they don't cross their paths at all so they both can go smoothly through without stopping at all. I do agree that roundabouts make the intersections safer, that's great, but it's at the cost of throughput but everybody pretends it's not true. Even the claim that the delay is reduced because cars would need to wait on traffic lights is dubious, because you can't just enter or leave a roundabout when there is heavy traffic through it that competes with your 'route' , roundabout is not equal for all entry points and doesn't distribute all of them equally. So you might wait just as long as you would waiting on traffic lights. Standard intersections are worse only if they have dumb traffic lights and the traffic is light, that forces you to stop and wait even though there is no competing traffic. But again, it's a case of fixing the lights and making them sense the incoming traffic instead of installing roundabouts.

> Let's say you have one car per hour, or any number of cars approaching in such a way that none of them gets close to the intersection at the same time.

That's not light traffic, that's basically no traffic. I don't think anyone bothers to build a roundabout for such intersection.

Roundabouts are for light to moderate traffic scenarios. Their main benefit is that they get drivers to slow down, which vastly reduces number of accidents and fatalities on the intersection. The effect on throughput is secondary, as the intersection was not congested anyway.

That claim of reduced fatalities is also getting outdated now, since the introduction of roundabouts with more than one line. Also accident rate for the cyclists is actually higher on roundabout than in a a standard intersection. So all in all, roundabouts are not as great as many insist and my beef with them and their supporters is that they keep bringing up the same talking points that were presented _before_ roundabouts started to be built on a massive scale and don't want to hear the empirical evidence about how these roundabouts actually work in practice.

I drove through some when visiting Aruba (Netherlands overseas province) and loved them. They seemed even safer than typical roundabouts and super intuitive

We drove through this last week. It's not done yet but it looks very confusing. If they were everywhere people would get used to it but with just one I think it may cause problems. And they can't be too common because they are absolutely huge compared to a regular intersection.

They are bigger but when people learn how to use them (only takes two or three encounters) then they massively increase throughput.

Here in the Netherlands, a roundabout is always the first choice and only if space is a limiting factor is a light used. But nowadays, the lights are really smart and can sometimes change to green for a single approaching car if there is space.

Also, roundabouts (as well as many city streets) have only 1 lane, and relatively narrow at that.

Which is ironic because roundabouts were initially sold as solutions making road intersections more safe, not as means of increasing throughput. The reduction of crashed and injuries comes from decreased speed of cars. So obviously it's at a cost of throughput

It's only obvious if you're confusing throughput with latency. Also, you're comparing with stoplights, a system where you often stop dead rather than slow down. So it's obvious to me that increasing safety and througput at the same time is very plausible.

That's indeed so obvious that in Europe there is a new trend of reverting roundabouts back to standard intersections. Because in reality roundabouts slow everything down to unbearable speed. EDIT: you make a mistake assuming that just because traffic going through a roundabout doesn't completely stop that it automatically means that the throughput is higher than a stop-and-go traffic through normal intersection. And also assume that traffic going through a roundabout never stops, which is simply not lined up with the observable reality

I'm not making any such assumptions. You're the one making bold claims about "obvious" causality, while I'm just saying it's not really obvious either way (and if you think that's a lie, check my phrasing more carefully).

Your initial claim: >So it's obvious to me that increasing safety and througput at the same time is very plausible.

Your current claim: >I'm not making any such assumptions

If you don't make any assumption how can you even say that something is 'very plausible'? Based on what exactly then? Gut feeling? If so then it's not 'plausible', it's just your gut feeling dressed in nice wording

> check my phrasing more carefully

"plausible" is not nearly as definite as "safety obviously comes at a cost of throughput", and is furthermore not a statement about causality, but a claim that improving safety and througput don't immediately rule each other out; a contradiction needs a strong proof, since so many things that appear contradictory turn out to be compatible with enough imagination. Absent that proof, compatibility is plausible.

But sure, maybe I should have put air quotes around "obvious", since there's no real obvious correct conclusions here. "Just your gut feeling dressed in nice wording" is another great way to describe your initial claim about roundabouts, too, which was my main point to start with.

I provided reasons why I think throughput would be affected, such as the fact that roundabout is a curved road explicitly designed to slow traffic down. With slowed down traffic approaching from all directions it is reasonable, hence plausible, to assume that the throughput would be negatively affected. You instead just reply with some sophistry and don't bring any arguments grounded in reality. Especially your statement, that 'absent that proof, compatibility is plausible' just highlights that you don't even know what 'plausible' actually means because something can't be plausible by default, without any reasoning or facts backing it up

I note you've moved the goalposts from "obvious" causality to "reasonable, therefore plausible" causality. Still, I continue to find your attempt at "grounding" unconvincing. The mere fact that cars must slow for a roundabout does not automatically make it lower throughput than one where they have to actually stop for some unspecified interval. Speaking of specification, if I was trying to be grounded, I would assume that which system has higher throughput depends on the implementation details and situation, notably the timing of the lights and how much traffic is naturally on the given road.

Details matter. You've been attempting to make generalizations irrespective of any of those details, and I'm saying they're not justified, or at best need much stronger evidence. But sure, I'm the sophist here. I'd ask you for "facts" to back up your claim, but you've already walked it back, so I guess I'm done.

Both can be true. If you have cars coming from all directions that can easily merge with each other, it makes sense that throughput would also be increased since the other 3 directions don't need to stop to make a left turn from any direction.

Safety might be factor number 1, but a roundabout will sustain higher traffic loads than a traffic light, assuming that all directions are being fed with equal amounts of vehicles. For this reason, a lot of arterial roads in NL still use traffic lights because they prioritize traffic moving in a single dimension (x or y, but not both). The smaller intersecting roads need to wait on the light during rush hour since the priority is traffic on the larger road.

When two roads of a similar size/traffic mix, a roundabout can be used to facilitate changing directions. Here is an example near Eindhoven in the south part of the country: https://maps.app.goo.gl/SYMnP9jwNEj1ytx2A

There's also a fairly large roundabout about 1-2km north of that intersection if you're interested. It's increased size provides more throughput and slows down drivers coming from the highway and allows a smooth transition down to the lower speed allowed within the city limits.

According to the article this was a statistical outlier for a specific type of collision, likely because of the long flat area around the intersection.

It's better to have a confused person drive the loop and have to circle back because they went the wrong way vs. initiative driver on a long haul zone out into intersecting traffic. Worse case they slam on their breaks for a rear end collision, which sounds less severe. I guess we shall see if it improves things, seems like they can't get much worse the way it is now.

Rear end collisions were the largest category of collision at the previous intersection, according to the local paper report I saw.

I expect that people will try to jump the curbs after they realize they're in the wrong lane. Some people will sadly do anything to avoid a wrong turn. But hopefully the collisions will be at lower speed.

I'm sure locals will get used to it but I think a big part of the problem with this intersection is that it's used by a lot of people who pass through very infrequently.

Driving is so dangerous and difficult that we have an entire licensing system set up, but we’ve also made it necessary to live, so we can’t deny anyone a license and we can’t do anything that requires drivers to learn anything new, because maybe they won’t feel like it. Wonderful society we’ve built here.

I’m not anti-roundabout but for $15 million could they have made it a highway interchange instead, raising one road, lowering the other to go under? Looking online it seems like it’d cost about the same amount for an interchange.

They do intend to build a highway interchange, but noted that since it will be at least 2028 before it’s finished, that they wanted to put in an immediate safety mitigation to reduce crashes for the next 5-10 years while that’s planned and built.

The article doesn't have any pictures of the roundabout, best I can tell. This article does, though:

https://www.ladbible.com/news/us-news/us-turbo-roundabout-ca...

I'm not sure why roundabouts are so uncommon in North America.

Where I live, at a 4 way small street intersection, two of the entrances have stop signs with a roundabout in the middle. At that point, you might as well get rid of the roundabout.

I think I live in a typical US CA city and there are dozens if not hundreds of roundabouts in this suburb. And I don't understand why you would have stop signs AND a roundabout. I am hoping someone can explain this feature to me. It just seems like extra chance for confusion and extra source of danger because of that.

> And I don't understand why you would have stop signs AND a roundabout

You shouldn't. It's a poor design choice to cater to Americans who aren't used to roundabouts and yield signs. It makes things less safe.

Wait, Americans aren't used to yield signs? Is this in general, or only in the context or roundabouts?

I've been driving in America for over 30 years and while I've seen them occasionally, they are very rare. And when I do see them, almost no one understands how they are supposed to work (go slowly until you know there is no one already there). They basically either don't slow down at all or stop like a stop sign.

It's not really covered when we learn how to drive. We get maybe a page on it in the handbook and one question on the driver's test. And then the road test almost never has one since they are so rare.

Your post as a sibling to mine cracks me up. It really underlines how different road design is in the Northeast to the rest of the country; I can hit four roundabouts to go three towns over if I picked my route to avoid the highway, and probably see another additional yield along the way. And it was one of the most important things drilled into us (Maine) during our driving lessons and exam, where we were taught “default to stop unless you know you’re clear”.

Not just northeast. GP is talking from their own narrow perspective. I've driven all over the country, and roundabouts (as well as yields) are common in some places and nonexistent in others. GP just seems to have a narrow experience.

Totally, they're elsewhere too! I was remarking more that in New England they're pretty universally How You Do Things, and it falls off pretty drastically once you get out of NY and PA.

Decently common in Metro Detroit. Few in my neighborhood and we also have a lot of boulevards which sometimes will have yields at every turnaround.

That would explain why there are so many stop signs in the US suburbs on intersection with excellent visibility and little to moderate traffic (at least, that's what I see in US movies). Must be super annoying to drive through. Where I live (Poland), stop signs are an exception, used only in circumstances where a mere yield sign is deemed too unsafe.

Yield signs, IME, are way more common in the Northeast than the rest of the country. They’re taught specifically in driving schools, too, or at least were when I attended, complete with “if you aren’t sure, treat it as a stop sign” (which might annoy drivers behind you but is the safer play).

We also have a lot of rotaries/roundabouts here, too, so you get a lot more practice.

You can't generalize across 340 million people across an an entire continent. Some regions have lots of yield signs and lots of roundabouts, some have very little of either one. The feds provide guidelines, but there is plenty of regional variation in preferences.

It's also a reaction to poorly placed roundabouts that are severely unbalanced and heavily used. Not every intersection is well suited to become a roundabout.

The only situation where I could see stop signs making sense is an unbalanced roundabout. It can be hard to get an opening to enter a busy roundabout that is dominated by cross traffic flow.

I have it even worse near my house. A roundabout with a stop sign at every entrance. It actually causes more problems than a four way stop sign, because people enter without signaling and then get mad when you assume they're going straight.

There is literally no difference between someone going straight and someone turning until they are right in front of you (unlike with a regular intersection where they would at least angle the front of their car to indicate turning).

Is this a "turbo roundabout"? https://maps.app.goo.gl/uxt1E7snorKLPxjC9

If so there are a lot more than 2 in the US.

While I don't see any pictures of the turbo roundabout in the article, it does say there are raised lane dividers that prevent traffic from changing lanes, so this does not look like a turbo.

There are a few multi lane and single lane roundabouts in my city (US,CA), none have raised dividers. Sounds interesting. Roundabouts in the right place can really help with traffic. In some places they're just dumb: 4 way STOP sign WITH a roundabout for example, yes they do exist, wish I understood why.

We have one of the dumb ones in NJ, circle at 202, 206, 28, with 202 going over it via a bridge. It is a very high stress round about where you can be stuck for some time waiting for an opening during rush hour, then you have to make a mad dash to another stop sign.

I was surprised to discover there were round about you are allowed to change lanes in. Here in Australia, all roundabouts are like this. If you enter in the outer lane you must take the first or second exit. If you enter in the inner lane, you must only exit on the second or third exit.

Doesn't look like it. A turbo roundabout is a spiral, not just multilane.

It seems it's a spiral that doesn't let you loop forever.

You could, you just have to keep changing lanes to do so.

The opening seems somewhat small to do a sideways lane change, as it designed for a more right-angle entry from the cross-road.

Of course the "obstructions" are low enough to drive over.

The American answer to everything. Just drive over it.

Yea, the point is to choose your direction in advance to minimize cross over traffic and lane changes. It will likely take a few weeks for people to get used to getting into the correct lane for their journey, but maps applications are already well equipped to handle these due to their increased use in Europe.

completely random thought: a roundabout is technically vulnerable to a DoS attack if enough drivers coordinate their efforts and just drive around in circles. Unless there is a law compelling drivers to choose an exit, that's technically different than a DoS attack by stopping in the roadway.

Roads and intersections have a similar DOS attack. Just "break down" in/on them.

You can DoS a road by placing a log or a long vehicle across it, no need to get fancy.

It's not the same, because driving in a circle on a roundabout is not obviously against the law

It is the same because if you’re blocking traffic they’ll stop you, law or no law. And almost certainly there is some general law against impeding traffic anyway.

You are not blocking traffic though because you are driving. That's the point. If driving can be considered blocking traffic then the police can also stop you for driving on a straight road because you also taking 'capacity' out

> You are not blocking traffic though because you are driving. That's the point.

Then if you’re not blocking traffic, there’s no DOS, and there’s no problem.

> If driving can be considered blocking traffic then the police can also stop you for driving on a straight road because you also taking 'capacity' out

They can and they will. If you’re impeding traffic in any way and it’s causing a problem, they will stop you.

This isn’t code. There aren’t loopholes. There have the power to stop you and they will if you’re causing trouble. Even if it’s “technically legal” they’ll still probably arrest you just to stop you and let you go later.

On this particular type of roundabout that would probably be hard to do: cars cannot circle on both lanes, outer lane will force you to exit.

> Unless there is a law compelling drivers to choose an exit

In most places it is illegal to go around more than once. In many places it's not even legal to make a "u-turn" by exiting at the same road you entered at.

I would guess that your best scenario is being nicely asked to stop by the local traffic police. But I bet that a much more likely category of scenarios involves very upset drivers that may not have a diplomatic answer.

Oh no, you found a loophole! The police will be powerless to stop you!

No, they’ll just stop you and arrest you for impeding traffic, and the judge will agree.

Real life isn’t code.

Not so fast. So how many times can you go around a roundabout for the police to decide you are obstructing traffic? What if you do it a few times and then leave round about only to come back a minute later?

Doesn’t matter. If it becomes a problem, they’ll stop it. If you’re going around constantly and it’s not causing a problem, no one will care.

> So how many times can you go around a roundabout for the police to decide you are obstructing traffic

https://i.imgur.com/LtS0oqI.jpg

Questions the judge will decide.

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