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Comment by peterept | Hacker News Reader

I don't know much about the logic used in self-driving cars - but I do wonder how they will handle roundabouts. We have a lot of them here (Australia) and you have to give way to a car that is approaching or entering the roundabout on your right - which often is opposite you. How will a self-driving car cope with detecting a vehicle behind the concrete barrier of a roundabout?

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No, the roundabout rule is that a vehicle entering a roundabout must give way to any vehicle already on the roundabout, or a tram that is entering or approaching the roundabout.

See the Australian Road Rules, Part 9: https://www.pcc.gov.au/uniform/Australian-Road-Rules-19March...

If you are approaching the roundabout and someone enters it from your left before you get there, you have to give way to them.

Isn't this what the original comment is saying though? Considering the cars are driving on the left-hand side of the road, cars in the roundabout are approaching from the right with respect to the vehicle, not the left. Or am I misunderstanding something unique for roundabouts in Australia? The way you describe it seems opposite of intuition that vehicles already within the roundabout do not have right of way.

The original comment says "you have to give way to a car that is approaching or entering the roundabout on your right", whereas the rule is that you have to give way to all cars already on the roundabout, without regard to whether they approached from your right or left. If they got into the roundabout before you got there, you have to give way.

This sounds really weird, Sweden also has roundabouts but I do not have to yield to anyone on the roundabout, only the ones that I will interfere with? Whether someone enters after or before me is really of no consequence. I am basically not allowed to enter if I will obstructing someones path of travel, with the additional caveat that both lanes of a multi-lane roundabout has to be free, since anyone in the roundabout is free to switch lanes.

In Australia you can not change lanes in a roundabout.

That's not true

> You can change lanes within a roundabout, but you must indicate and give way to other vehicles. http://www.roadrules.rsc.wa.gov.au/road-rules/roundabouts

edit: and NSW too, to make it clear this isn't just "oh WA"

> Be careful if changing lanes in a roundabout, particularly when leaving http://www.rms.nsw.gov.au/roads/safety-rules/road-rules/roun...

>I am basically not allowed to enter if I will obstructing someones path of travel,

Yes, you just described how yielding works everywhere. You enter unless you will block someone. There is nowhere in the world that you yield to someone who isn't going to hit you, that's just called a stop sign.

Things like that may vary from country to country, though. In Austria, roundabouts do not have a special rule and therefore a car approaching the roundabout theoretically has the right of way. But pretty much any roundabout has a yield sign, I've never encountered one without a yield sign at the entrance. Doesn't mean that there can't be a roundabout that does not have one.

As you described, the default is to yield, and so the vehicle can always yield and signal its intention to do so by breaking slowly. And I agree, there may not always be a sign (a storm or driver could knock it over), so the default should always be to yield.

> you have to give way to a car that is approaching or entering the roundabout on your right - which often is opposite you. How will a self-driving car cope with detecting a vehicle behind the concrete barrier of a roundabout?

How does a human driver detect a vehicle behind a concrete barrier?

Either humans can see it and the intersection makes sense, of humans (and machines) can't see it and the whole setup does not make any sense.

In Mountain View, I once saw a Google/Waymo car trying to cross traffic and turn left onto Rengstorff Ave, which is a pretty busy street in the evenings. As a human driver, I wouldn't know how to do it unless there was a miraculous break in traffic, I would have just turned right and go the opposite direction and make a u-turn elsewhere. So like you, I'm curious how it handled that situation as well.

In Europe we have a lot of roundabouts that work the opposite way, priority is given to anyone inside/exiting the roundabout, which would seem easier to handle for automated systems.

I think that's what is meant, remember Australians drive on the left.

Also in Europe it depends what road signs are at the roundabout. They have no special status in my country and can be looked as a "T" intersections connected to a circle. In most cases there is a yield sign for the cars approaching the roundabout so the cars already on it have right of the way, but it is not the case for all roundabouts. Also, some roundabout allow exit from the two rightmost lanes, others just from one—it also depends on signage.

If they are still on the other side of the roundabout (and there are no other cars), can't you safely enter the roundabout anyway?

My understanding is that the goal behind a roundabout is to create an intersection where any vehicles that enter are traveling in a similar direction, improving the capability of people to avoid crashing and reducing the seriousness of crashes that do occur between vehicles.

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