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Comment by fijal | Hacker News Reader

4-way stop turn-taking is a problem that does not exist in europe btw

4-way stops exist in Sweden. Quoting from Wikipedia at http://sv.wikipedia.org/wiki/Stopplikt :

> Vissa korsningar har en stoppskylt vid varje väg, ett så kallat flervägsstopp. Det innebär att alla som kommer till korsningen måste stanna, oavsett vilken väg man kommer på. Tanken är att man vid flervägsstopp ska ta ögonkontakt med medtrafikanter för att på så sätt komma överens om vem som ska köra först.

Or my translation "Certain intersections have a stop sign at every way, a so-called multi-way stop. This means that everyone who comes to the intersection must stop, despite which way they come from. The thought is that people at the multi-way stop will make eye contact with their fellow drivers in order to come to an agreement on who shall drive first.

(Apparently the actual law says "ömsesidig hänsyn" - "mutual consideration.")

That said, they aren't anywhere near as common as the US.

Do you actually have them in Sweden? I was taught similar rules back when getting a driving licence, but it doesn't neccessarily mean that such intersections exist - I was told about intersections that were like that in 1960ies, but those spots have traffic lights now.

I drive through one a few times a week, in Västerås, Sweden.

I biked through one yesterday, in Trollhättan. If you do an image search for "flervägsstopp" you'll find several images, including this one which is specifically a four-way stop: http://www.trafikmagasinet.nu/art090503.htm .

If you're more curious, see http://www.trafikverket.se/PageFiles/3038/komplett_slutrappo... , among others. That one talks about how they were tested out during the 1980s, and by 2007 there were a few hundred in the country.

We have a lot of them in Trollhättan. And roundabouts, holy shit the amount of roundabouts in this city.

Hej! Another Trollhättebo! Yeah, I actually passed a couple on my ride, though I only mentioned one. As an American my baseline is the number of 4-way stops in the US. I've only lived in Gothenburg and here, which gives a poor sampling bias.

Well, good luck to Google and Volvo in making the eye contact thing work...

It could use laser eyes to blind the other drivers. :)

Oh? At least in Germany it's that you have to yield to a driver to the right (ignoring priority roads) but if you have an intersection of non-priority roads and a car from each direction someone has to make a decision to go first, otherwise it's a deadlock.

Unless I misunderstood the problem.

Europe doesn't generally use 4-way stop signs (http://en.wikipedia.org/wiki/All-way_stop) in the traffic regulations; intersections tend to be either regulated, or with one road designated as the priority, or as roundabouts, not like this.

I've driven a bit around Europe, but I have never seen a single such intersection in my life - if they exist, they must be rare.

Of course, "if you have an intersection of non-priority roads and a car from each direction" then it's the same, but in practice it seems that 'they' make sure that such intersections are only in extremely low-traffic places where you'll very rarely see another car at the same time.

In creating an autonomous car, successfully handling those rare edge cases are going to be the thing that differentiates success from failure. Roundabouts and Michigan left turns are rare in most places in the US, but an autonomous car would still have to be able to handle them.

In Sweden as soon as you're in a residential area or out in the countryside, unmarked priority-to-the-right crossings are the norm. And if cars from all directions in a crossing arrive at once, you end up with an ambiguous 4-way stop situation.

In the countryside you'll often see this warning sign to remind you that "just because your road is bigger and faster than the one you're about to cross doesn't mean you have priority" http://www.transportstyrelsen.se/Vagmarken/Varningsmarken/A2...

Actually it does exist but is rarely used : http://en.wikipedia.org/wiki/All-way_stop

In Europe you can have ambiguous situations with the priority to the right, where you are supposed to be courteous and wave the driver if both (or more) have the right of way.

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