Hacker News Reader

Comment by burlesona | Hacker News Reader

One of the best ways to eliminate left turns is to replace four way intersections with roundabouts. This has the advantage of working even where there isn’t a grid to facilitate the “3 right turns” strategy.

For a great description of why this is so effective, see the recent freakonomics podcast: https://freakonomics.com/podcast/roundabouts/

View on HN

As a French, it's really surprising to see how other people from other countries aren't used to roundabouts. I really like how diverse roundabouts are here. Some are arranged like gardens, some have flowers, some have sculptures, some have decorations made by the local school.

A funny anecdote: we used to go to Pontarlier from time to time because our grandparents had a house here. Every time we went, we saw that [1] awful roundabout. A few years ago, it was elected as the ugliest roundabout in France.

https://france3-regions.francetvinfo.fr/image/Zb2s5pOo3hJVEK...

(Edit: I've edited the link to point the correct roundabout. The previous link was https://sf1am.autojournal.fr/wp-content/uploads/sites/9/2018...)

Place de l'Etoile in Paris is one of the most famous roundabout.

http://www.champselysees-paris.com/images/sightseeing-images...

The French are not very good at using roundabouts IME, they don't indicate which exit they intend to use.

Just making sure this isn't a misunderstanding: Roundabout signaling laws and conventions vary between countries, and in some countries you're supposed to signal your intent both entering and exiting the roundabout, while in some you only signal at the exit. I'm not sure about French conventions, but in some European countries (Germany, some Eastern European countries, probably others) indicating before the roundabout is actually illegal.

French conventions are to signal when you're exiting at the next exit.

I drive in Italy and Canada, the signaling is very different. In Italy you would signal left to indicato "entering", then signal right when about to leave.

In Canada you signal before entering, and signal right when you plan to exit right, left when left, nothing when going straight.

This assumption doesn't work for Italy wherte there are roundabouts with 5 or more roads involved.

You know, it's kinda cool. If that's the worst roundabout in France...

Is that a thumb?!

Sorry, this was the wrong link but yes this one is a thumb.

Roundabouts in the busy city center would be terrible. Where roundabouts fit best is in intersections with low demand, because they have low capacity, and there's no reasonable way to increase capacity.

If it's the urban core busy city center where there are skyscrapers right up to the lot line, there's no room for a roundabout unless you're willing to make 'round a bumps' or carve some footprint out of the buildings at traffic level.

If it's the busy city center where you've got four lane surface streets intersecting with each direction having two straight through lanes, one right turn lane and one or two left turn lanes, a roundabout is never going to manage that kind of throughput by forcing all those people into a single lane to get into the roundabout at low speeds.

You may have fewer collisions, and of course very few of them will be during left turns, but you'll also reduce the utility of the roads connected to the roundabout, which will likely move traffic to other roads. Also, a collision in the roundabout stops the roundabout, which makes it hard to respond if people are injured or vehiclea disabled.

Traffic signals with 'protected' lefts don't stop people from going against the signal, but they do stop a lot of people from trying to make a gap that they really shouldn't. Sometimes a three-way signal timing pattern is appropriate; for the main direction, opposing traffic has greens for straight simultaneous (with cycles for protected left if appropriate), and for the other direction, each side gets a green for straight and left one side at a time.

Many roundabouts are multilane and the design in general has higher throughput than a typical intersection because drivers don’t need to stop. Traffic is always flowing.

You are right that they require a slightly bigger footprint.

https://www.acsengineers.com.au/2016/08/22/roundabouts-vs-tr...

The biggest roundabout I’ve personally driven was an intersection of 2 freeways and a major city throughfare. 5 lanes in the circle itself, all at speeds up to 90kph.

They’ve since added stoplights on it because people were being dumb and blowing through the whole thing at ridiculous speeds.

https://images.app.goo.gl/jpzgxUyQDoqe81y38

You should visit the UK and get a native to drive you around some city centres. We have the full range of roundabouts from massive, traffic light controlled, multi-lain and chain-linked junctions, down to tiny roundabouts that are little more than a circular bump in the road.

It's rare that I stop at a junction that requires me to cross a traffic flow, lights or no lights, that I don't wish that a roundabout had been put there instead.

Collisions can at times bring a roundabout to a halt, but more often than not, people just use common sense and move around any obstacle, while maintaining as much lain discipline as they can.

Cyclists, so long as they behave as if they are cars, also rarely have issues at roundabouts. I'm quite accustomed, in my area, to following a cyclist around a roundabout, paying attention to their hand signals, and giving them plenty of space.

Basically, it comes down to training and practice. In the UK, if you can't handle a variety of roundabouts, you'll fail your driving test.

> I'm quite accustomed, in my area, to following a cyclist around a roundabout, paying attention to their hand signals, and giving them plenty of space.

As a cyclist, sometimes in roundabouts, this is something that many drivers need to be more aware of. In particular, depending on the roundabout size, the entry angle, and the car, someone's A pillar may completely obscure a cyclist.

Also, while a great solution for cars, in populated areas, roundabouts can be tricky for pedestrians to cross. Also not aided by the fact that at least in Germany many motorists have no clue about the exact rules (yield to crossing pedestrians and cyclists when exiting the roundabout because that's effectively a turn). The best solution in this regard still seems to be to put zebra crossings all around the roundabout, along with traffic islands between the lanes entering and existing the roundabout. That makes it sufficiently safe for people and bikes to cross and sufficiently obvious to drivers how to behave. But that takes even more space.

Manchester is full of them. Majority of junctions on the M60, the motorway circling the city, have roundabouts after you come off / before you get on.

In fact, there are two roundabouts in Worsley/Walkden. Though those cause a huge amount of traffic in rush hour.

Pretty much any journey I take in the UK involves at least one and could be upwards of 10 to 20 for longer distance drives.

Roundabouts can be made to handle high-traffic - supplemented by stop lights if necessary - satellite view Tijuana for some examples.

The thing is until people are used to them - which can take years if not decades - they can be slower. And they can be hard to retrofit into older locations. In cities it may be better to turn streets to one way (making all turns “right turns” effectively).

Valencia, Spain is another example. I was confused in the beginning but after a day or so it felt comfortable. They have ~4 lanes in the roundabouts.

Edit: 7 lanes in this particular one: https://goo.gl/maps/HpFvtHeFTC5om81NA :o

CDMX as well, although some of their roundabouts move in both directions, which is both insane and appeared to be the worst of all worlds.

Reminds me of that study showing you could have computer controlled cars weave through an intersection without stopping and it worked fine but the passengers couldn’t stand it.

So devise an automated devil’s traffic circle with cars going in all directions.

Cities in Europe are full of roundabouts in the busy city center, we don't have four way intersections. It's not terrible; it's safer. They handle the throughput better than intersections, because the flow is usually uninterrupted.

There shouldn't be cars at all in busy city centers.

I'm a little skeptical that it would be safer for pedestrians and bikes. Bikes need to merge with traffic already in the roundabout instead of simply going straight through an intersection, and pedestrians would need to always check for oncoming cars rather than being able to mostly rely on lights telling them when they can cross.

But then most of my experience with roundabouts is with large, multilane roundabouts so the traffic is still pretty fast - maybe smaller roundabouts with significantly slower traffic would be safer than I'm picturing.

Proper Dutch-style roundabouts have the path for cyclists that follows the sidewalk, not the car lane.

https://commons.m.wikimedia.org/wiki/File:Alternative_dutch_...

Multi-lane intersections on major roads should just have a left-turn lane with a separate signal phase.

Unless it's a motorway-style roundabout with many multiple lanes and high velocity traffic, I much prefer to "pretend to be a car" when I cycle through roundabouts. The busiest roundabout I regularly cycle through has 2 lanes and 6 roads intersect at it. I can't imagine wanting to use it if I had to operate outside the basic rules of roundabouts.

Something like this?

https://www.youtube.com/watch?v=FR5l48_h5Eo

Mode separation for motor, bicycle, and foot traffic; all traffic crosses as close to 90 degrees as possible (for visibility reasons); priority markings on pavement; speed bump on one of the entrances to slow traffic; and a lot more features I couldn't tell you about.

( I sometimes watch https://www.youtube.com/c/NotJustBikes/ , but I'm no traffic expert )

This is incorrect. To a rounding error all the roundabouts I have encountered (in the Netherlands, where I live) have the cycle lane follow the car lane, and give cyclists right-of-way over the cars. You'll occasionally see one where the cycle lane is separated from the roundabout, but I only know of one from the top of my head.

If you have a bike path alongside the car lanes, they seem to work really well. See this one for example - the red paved path is for bikes: https://i.redd.it/1vfvbvntky411.jpg

The bike path crosses before the point where cars merge in, so the driver's attention isn't split. Also, it may not be obvious from the picture, but the car lanes are raised to the level of the bike path where they intersect.

The problem with these roundabouts is that a car driver cannot simply "exit the roundabout". They have to watch front, side and rear for cyclists. IMHO a roundabout should only ever impede traffic on entry. Once you're in the roundabout your journey around and out should be entirely unimpeded. Following the basic principles, there should never be a situation where a vehicle is going around the outter circumference of the roundabout blocking a vehicle from exiting. (Even a bicycle)

Only the front in theory: the crossing with the bicycle path is fairly close to 90 degrees. Even so -in practice- you should be checking side and rear anytime you make any turn on any kind of intersection (you fail the dutch driving exam if you forget even just once).

I agree that even ideally-er the journey out should be 100% unimpeded, but in practice this setup seems to work ok. See also video I posted for you, above. :-)

What if they moved the bike/pedestrian crossings to further along the lanes away from the roundabout? This would give more room for the cars to exit the roundabout without encountering immediate cross traffic, and more "collection space" on the exit itself so if a driver does have to stop to let a pedestrian/cyclist through they don't impede the roundabout traffic.

Posted video link of this type of roundabout in action just above ( https://news.ycombinator.com/item?id=27415631 )

There's just sufficient space for 1 car to tuck in each time.

Note that the priority here is not necessarily to maximize car throughput at all costs; but to ensure safety for all modes of traffic; and to do so inside a given amount of space and cost.

Given a different set of parameters, a different intersection type might be chosen.

(+) That said, note in the video that there's a significant number of people using the bicycle lane and pedestrian path; I think they're carrying more people than the car lanes here. I'm not a traffic expert, but forcing the denser traffic to take a longer route in favor of the less dense traffic does not seem like the right choice here. ;-)

It seems to work during that 5 minute segment, but at 1.45 it looks like this system could get gridlocked. If vehicles are blocked from exiting a roundabout for long enough, there's a risk that the whole thing will fill up. When this happens, it can only get unblocked quickly if the vehicles blocking the exits wish to leave via those exits. Edit: nope, the system can continue to move, but when more exits are blocked, the system throughput drops sharply to zero. I'd love to see this roundabout during rush hour.

For cyclists safety, this system works because the cycle lane is so far outside the vehicle lane, and it is right before pedestrian crossing. Most of the roundabouts with bicycle lanes that I have encountered, they just used a different coloured tarmac at the edge to show cyclists where they should risk their lives. They're not at 90 degrees to the cars, they're literally side-by-side. In that situation, cyclists are in greater danger of getting side-swiped by a car exiting the roundabout.

Uh I live next to a roundabout (single lane) and it’s the safest thing ever. I’m guessing you’re American?

I you want to see a country that appears to be extremely fond of roundabouts, you should come to the Netherlands. In the past 20 years a high proportion of crossings has been replaced by roundabouts.

We do not always have sufficient space, especially in city centers. The normal solution there is to make traffic one-way only. I do not know if they consciously try to avoid left turns, but it would seem to make sense.

I would certainly advise visitors not to take their car when visiting a Dutch city center. Using public transportation is a lot easier (and cheaper).

Two wrongs don't make a left, but 3 rights do.

Try that in this city :)

http://szczecinblog.pl/wp-content/uploads/2011/07/historyczn...

I've visited it a few years ago and I found myself accidently going in circles constantly :)

Round and round we go... You just wanted to take the very scenic route to make sure you didn't miss anything. ;-)

Not hard to get into that situation here if you don't know which way you are going: https://www.google.com/maps/@48.6302508,-123.4122954,275m/da...

Came here to say this. Yes, it can slow down traffic in some cases but preemptively installing roundabouts in little-used intersections next to parks can save headaches of wandering kids getting flattened.

My lengthy driving experience in and around the New York area has more than convinced me that widespread inability to merge would make roundabouts here extremely difficult to implement. The few that do exist are usually littered with people who have stopped completely or are trying to cut across three lanes of traffic because they don't know what they are doing or where they are going.

As a pedestrian and a cyclist, please, no. I don't trust crossing a lane of traffic unless traffic is fully stopped, and nobody expects to stop in a roundabout, so I don't even feel safe using the crosswalks and hoping that the traffic will yield. Let cars come to a complete stop.

I think this is a pertinent point to the way roundabouts are implemented and used in North America. Cars are almost always going too fast on their exit from the roundabout, which renders the "yield" sign on the exit side crosswalks defunct. Not to mention that if they do yield to a pedestrian there, the crosswalks are close enough to the roundabout that they might be impeding traffic in the roundabout itself.

The crosswalks in the roundabout need to be moved away from the circle itself significantly (10-15m at least) for roundabouts to be safe for cyclists and pedestrians. At least for the way they are used in North America IME.

It depends a lot on the country you are in. In the Netherlands pedestrians and cyclists normally get priority, because the car is making a right turn while the other groups are continuing in a straight fashion. What probably also helps is that when a car is involved in an accident with a pedestrian/cyclist the default assumption is that the car driver is guilty.

Roundabouts are great when people know how to use them to their full effect. They are beginning to become more common in the US but no one knows how to use them. People will treat it like a four way intersection until it is completely empty. Drives me nuts.

I live close to a place that has only roundabouts and zero intersections. It's just terrible. Very easy to congest and once the congestion reaches the previous roundabout it's game over. Everything stops.

But people don’t know how to use them and just make it a free for all. Look no further than the Boston metro area for how this actually shakes out.

15 to 20 years ago when roundabouts were first introduced to where I live (southern Germany), people were pretty terrible at using them.

After about 5-10 years, people have gotten the hang of it, new drivers were properly educated in driving school, now they work fine.

You've got to have a little patience, and actually expose people to it, then it works out fine.

This is a self-fulfilling prophecy. People don't know how to use them because they never encounter them. Once they've been around for a while, people will encounter them and learn how to use them.

There are lots of roundabouts in the Boston area (where we call them rotaries). People encounter them regularly and STILL don't know how to use them. Although recently there have been great strides made in using lane markings to steer drivers through more effectively.

If Americans can put down their mobile phones and concentrate on the driving.

Swindon's 7 rings of fiery death doesn't need right turns or stop lights.

Reply on news.ycombinator.com