Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

We're excited about our new roundabout

wsdotblog.blogspot.com

Post reply on HN
Print view View original

161–170 of 316 posts

Re: We're excited about our new roundabout

#161

Post by shiroiushi »

lmm wrote: post #100
bnralt wrote: post #95

Earlier quoted context omitted.

Online I see this mentality that roundabouts are great no matter what and it seems really strange to me. It really depends on the design of the roundabout and the traffic conditions. Where I grew up there are a lot of roundabouts, but many of them are so dangerously designed I started actively avoiding them. It’s not that you can’t poorly design a four way stop, but it seems to be much less common, for whatever reaso…

They absolutely are. Even if they don't prevent all collisions, they turn T-bones into glancing hits and so save a lot of lives. The worst roundabout beats the best 4-way stop any day of the week. Sometimes there really are easy answers.

>Even if they don't prevent all collisions, they turn T-bones into glancing hits

No, they don't, at least not in America. When you let American traffic engineers design a roundabout, you get this: https://www.google.com/maps/@38.8643875,-77.2755474,583m/

Re: We're excited about our new roundabout

#162

Post by PetitPrince »

OptionOfT wrote: post #130

The biggest problem with roundabouts the main direction can starve the lesser-used entrances. Imagine the main road going North-South, and you're entering via East to go South. Because of never-ending traffic going North-South you just don't get to enter.

You can have several lanes so that the outer one favor going to the nearest exit:

https://maps.app.goo.gl/v76ajKvXhzfAdGZ29

Or you can also have dedicated lane that only go to the nearest exit:

https://maps.app.goo.gl/1G2cJf1pWrBkEE5b8

Re: We're excited about our new roundabout

#163

Post by asib »

necrobrit wrote: post #149
bane wrote: post #108

This is oddly timely. I'm travelling in Europe at the moment and have been covering a lot of area with a lot of roundabouts where they would be signaled or signed intersections in the US. They definitely make traffic flow smoothly and I've noticed a few areas where they are used to eliminate dangerous left turns at places like parking lots, you leave turning right, hit the next roundabout to "uturn" then head back th…

The preference for 4 way stops in a country that otherwise prioritises traffic flow so much is really jarring. Traffic lights too to some extent. About 5 years ago my wife an I were doing a California road trip. At one point on a relatively rural road -- I think it might have been Dry Creek road heading into Napa but cannae mind exactly -- we got stuck in traffic for around 45 minutes. We thought there must have been…

4-way stops are bizarre to me having grown up in the UK where roundabouts/intersections with priority given for one direction are trusted and reliable traffic-calming measures.

I think one of the reasons a 4-way stop might be introduced is to improve safety where there was previously a 2-way stop (that people would blow through). I came across this in Canada recently. All I can say is the UK has drastically lower traffic-related deaths than Canada [0] and I think I've seen 2-3 stop signs in my entire life. I imagine North America's pedestrian hostility is a piece of this puzzle.

Don't get me started on North American highway interchanges. The UK's roundabout junction system is far superior, in my opinion.

[0]: https://en.wikipedia.org/wiki/List_of_countries_by_traffic-r...

Re: We're excited about our new roundabout

#164

Post by alt227 »

jen729w wrote: post #157
svl wrote: post #147

No discussion about roundabouts can be complete without a mention of the (mostly) Dutch "turbo roundabout", where the lane you take going into a multi-lane roundabout depends on where you want to exit, and you can't / are not allowed to switch lanes while on it: https://wiki.openstreetmap.org/wiki/Tag:roundabout%3Dturbo https://en.wikipedia.org/wiki/Roundabout#Turbo_roundabouts https://www.arcadis.com/en-us/knowledge…

Similarly this is a mandatory mention. https://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempst...

Oh come on the Swindon one is the original and best :)

https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)

Re: We're excited about our new roundabout

#165

Post by asib »

svl wrote: post #147

No discussion about roundabouts can be complete without a mention of the (mostly) Dutch "turbo roundabout", where the lane you take going into a multi-lane roundabout depends on where you want to exit, and you can't / are not allowed to switch lanes while on it: https://wiki.openstreetmap.org/wiki/Tag:roundabout%3Dturbo https://en.wikipedia.org/wiki/Roundabout#Turbo_roundabouts https://www.arcadis.com/en-us/knowledge…

This is literally just how you're supposed to go round any roundabout. Right lane if you're going straight ahead or right (to any extent), left lane otherwise. Anything else _will_ cause crashes, because vehicles will necessarily have to cut across each other to exit the roundabout.

The "turbo roundabout" might make this explicit, but it's not different.

Re: We're excited about our new roundabout

#166

Post by lozenge »

shiroiushi wrote: post #161
lmm wrote: post #100

Earlier quoted context omitted.

They absolutely are. Even if they don't prevent all collisions, they turn T-bones into glancing hits and so save a lot of lives. The worst roundabout beats the best 4-way stop any day of the week. Sometimes there really are easy answers.

>Even if they don't prevent all collisions, they turn T-bones into glancing hits No, they don't, at least not in America. When you let American traffic engineers design a roundabout, you get this: https://www.google.com/maps/@38.8643875,-77.2755474,583m/

That's... Not a roundabout. It would be funny if it weren't so scary.

Re: We're excited about our new roundabout

#167

Post by lozenge »

Aeolun wrote: post #124
davidgay wrote: post #121

Earlier quoted context omitted.

You can actually screw them up: by our house (in California) they replaced a 4-way stop with a roundabout with no signaling on 2 of the ways, and a stop on the other 2. An absolute disaster, as the 2 ways without the stop assumed they had the right of way over people already in the roundabout. After the neighbourhood complained, it's now a roundabout with 4 stops (not ideal, but not dangerous either).

What should I imagine when you say roundabout with 4 stops? Isn’t that just an intersection that looks like a roundabout without functioning like one (entirely negating the point)?

I guess drivers just don't realise they need to slow down or give way to anybody unless there's a stop sign, traffic light or they're turning into a different road.

Re: We're excited about our new roundabout

#168

Post by tda »

asib wrote: post #165
svl wrote: post #147

No discussion about roundabouts can be complete without a mention of the (mostly) Dutch "turbo roundabout", where the lane you take going into a multi-lane roundabout depends on where you want to exit, and you can't / are not allowed to switch lanes while on it: https://wiki.openstreetmap.org/wiki/Tag:roundabout%3Dturbo https://en.wikipedia.org/wiki/Roundabout#Turbo_roundabouts https://www.arcadis.com/en-us/knowledge…

This is literally just how you're supposed to go round any roundabout. Right lane if you're going straight ahead or right (to any extent), left lane otherwise. Anything else _will_ cause crashes, because vehicles will necessarily have to cut across each other to exit the roundabout. The "turbo roundabout" might make this explicit, but it's not different.

It's only the difference between CI enforcing code style vs manual PR reviews that have a checkbox for code style. They accomplish the same, but one is infinitely better.

Re: We're excited about our new roundabout

#169

Post by eCa »

teractiveodular wrote: post #142
tmnvix wrote: post #140

Roundabouts get a lot of praise whenever they're mentioned, and from a traffic flow perspective that's understandable - if by traffic you mean motorised traffic. For pedestrians and cyclists they are worse than the alternative (lights - or even a simple intersection) in my opinion. > Making a roundabout for everyone ctrl-f "walk", "cycl", pedes". Nothing.

Citation needed. As a cyclist I prefer roundabouts: they're faster than lights and don't rob my momentum, and they're safer than uncontrolled intersections/4-way stops because all the cars are coming from the same direction. Caveat: this is for simple, single-lane roundabouts. Multi-lane roundabouts are gnarly for cars and worse for cyclists.

In my experience[1], if there’s no bike path roundabouts are better, in particular for left turns. But on a bike path they are usually not much fun, basically requiring negotiating with drivers 270 degrees apart at the same time.

My preferred roundabout is separate bikepath that joins the road just before and is a part of the same surface, usually found in bike friendly places.

[1] 60000+ km throughout Europe

Re: We're excited about our new roundabout

#170

Post by Plasmoid2000ad »

fransje26 wrote: post #154
urbandw311er wrote: post #143

UK reader here (we are pretty much 'all in' on roundabouts) I'm reading this and wondering how they'd cope with the 'Magic Roundabout': https://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempst... Even UK drivers struggle a bit with this one!

As the credited inventors of the modern roundabout, I've always wondered how the UK traffic planners managed to misunderstand their own creation to the point that they come up with such designs.. An other baffling design I've encountered in the UK is a roundabout with traffic lights half-way through.. Wasn't the concept based on removing traffic lights to fluidify traffic..? As a whole, if designers come up with far-…

Roundabouts with traffic lights are a bit of a failure alright - and the larger ones are i'd argue not roundabouts at all - they just share the shape.

I believe traffic lights are always trying to solve a capacity issue - where the roundabout has hit it's maximum capacity and is suffering some throughput issue, which tend to sort of get exponentially worse. With traffic light sequencing, particularily dynamically, there is always a way to even out the flow - prioritize a flow that is backing up undesirable or give a particular entrance fair chance to enter the roundabout.

Though once there are traffic lights on every entrance, plus traffic lights mid roundabout and some/all exits, and explict lane markings and merges I think it's not a roundabout.

Slowing down is important though, as it give drivers time to think and react. Whether they choose to use that time correctly is a problem, but hopefully some or all of the other drivers can use patience and avoid an accident. Where accidents happen, I see it's often from mistakes from two drivers, and it's relatively low speed. Better still, accidents are at shallower angles, so injuries are rare. I've heard an statistic that could well be fake that roundabouts have more accidents, but significantly better outcomes overall.

Post reply on HN