Roundabouts: A Misunderstood Intersection | Hacker News Reader

Roundabouts: A Misunderstood Intersection

wabe.org

26 pointsgruez17 comments

My favorite local junctions is the magic roundabout in Hemel Hempstead, UK [1]. A traffic circle (roundabout with traffic lights) would have also worked for this junction, but instead they used a ring of mini roundabouts, one placed at each entrance/exit road, connected to one another by short dual carriageway sections.

This allows for traffic to flow both ways around the circle, while forcing drivers on the "roundabout" to slow down to navigate the mini roundabouts, while not forcing people to stop completely for lights. In practice it works incredibly well, maintaining a steady flow of traffic even under heavy congestion. IMO it works far better than a controlled roundabout, and it a lot more fun!

It's also a favorite for driving test examiners...

[1] https://www.google.co.uk/maps/place/Hemel+Hempstead,+Hertfor...

Minor point, a roundabout with traffic lights is a gyratory

I did not know that term, thanks!

2. As you exit, it's nice to use your turn-signal to alert the driver behind you.

I always thought the main point of using your turn-signal is (apart from that it is the law, at least where I live) to alert the ones in front of you, i.e. so that drivers wanting to enter the roundabout know they can do so already without having to wait for you because you're leaving it anyway and hence leave a void where the next car can enter?

In the UK, where roundabouts are common, there is an added complication of an inside and outside lane.

If you are taking the third exit (turning right) you have to make your way into the inside lane on entry and back across the outside lane on exit.

Doing this without indicating would cause chaos. As driving standards have worsened over the years this has become an all too frequent problem.

One of the nicest sideways-thinking pieces of design I've seen in traffic junctions in recent years has been spiral lanes, which deal with this beautifully. Unless you change your mind while actually on the roundabout you hardly ever need to change lane on one of these.

You select your lane as you approach the roundabout based on which exit you want to take. You then just follow the lane markings, which take you on to the roundabout, around it, and out your desired exit.

Here's a picture (of an unusually complex one; they're usually simpler than this): http://www.whereitis.co.uk/_Media/green-bridge-spiral-rounda...

Here's another example in Oeiras, Portugal: https://www.google.co.uk/maps/place/Oeiras,+Portugal/@38.696...

I'd never enter a roundabout with an approaching car signalling that they are intending to exit. Some people wrongly signal early (they're actually intending to leave at a subsequent exit), some set their indicator (turn-signal) on when they entered the roundabout and just keep it on, some are indicating because they changed lane on the roundabout. I've seen too many side-on collisions in these situations.

Basically, I drive defensively and don't trust other people's signalling. (UK driver)

Agreed - that's how I was taught (in the UK) - never assume anything about the other driver's intention but wait until that intention is clear. In other words, turn signals mean nothing unless you have confirmation by action.

I'd never enter a roundabout with an approaching car signalling that they are intending to exit

Too late to edit but thinking of it, neither do I. It just allows you to start planning/reacting earlier.

If they are signaling right, towards you, you obviously do not enter. But what do you do if there's no signal and they are riding the inner lane ? Do you plunge right in only to see they were after all about to exit, just forgot to signal ? Very risky.

I see the signal as a way to communicate inside the circular road, where normal lane rules apply: you keep your lane, and if the lane in right is free, you can switch to it after signaling. Repeat until exit.

Also, a left signal before entering is useful: it says you are taking the 3rd or more exit, and that you will make a tight turn around the center, with slow speed. This way, people entering after you can plan to pass you on your right and continue forward.

These lefts and rights take a bit of parsing because UK drive on the left so their signals would be different.

This sounds completely alien to me and I'm from a country that uses roundabouts extensively. Indicating before you get onto the roundabout and keeping that indicator on the whole time just sounds very wrong. Also changing lanes at will is odd. You join into the inner lane if your exit is after 12 o'clock, and then indicate your exit after you have passed the one before your intended exit. 'Passing' on a roundabout is also a strange phenomenon I've never really seen before (unless it's unintentional of course)

Roundabouts have started appearing in Thailand, a country where most of driving population do not hold any form of driving license and had only minor handed down informal training, the results are comical, although there is probably some scientific value that can be taken away if studied seriously. The most common observation I found is that most give way to entering traffic (i.e. they stop in the roundabout), there are of course less common instances of going around with hazard lights on, and going the wrong direction, and even just driving over them completely ignorant, by less common I mean <20% not the exception you witness elsewhere. If you're on holiday in Koh Samui, Thailand and from a country where roundabouts are popular then this location https://www.google.com/maps/place/Ko+Samui,+Thailand/@9.5340... will provide a good few minutes of free entertainment, just don't stand too close to the road, luckily though an ambulance is usually stationed a few metres away. Unfortunately this roundabout doesn't work (in terms of optimal traffic flow) for the reasons above and unlike "a north Georgia town" education isn't going to be possible when they have no license or training, and more importantly not a care in the world.

The problem with roundabouts in the states is circular:

Nobody likes them or knows how to use them so they need to have tons of signs and restrictions on them so people don't kill themselves or go around the wrong way (the ones near my parents house actually have stop signs at every entrance). This complicates things and stops them working very effectively, resulting in people not liking them or knowing how to use them right.

If they had simply dropped them in place without comment, people would have spent a few weeks crashing into each other and then figured it out and they would work fine.

Mythbusters did a '4 way stop' vs roundabout comparison a few years ago[0]. It was interesting to see American drivers who were mostly unfamiliar with roundabouts warming to them.

[0] http://www.wimp.com/testroundabout/

One thing this and the comments really highlight is how different driving styles are in different countries. I wonder how much this is responsible for traffic accidents?

As an example:

- In the US people aren't taught (or don't care about) lane discipline, where as in Europe you will make people very angry driving slowly in the inside lane [0]. As such undertaking is usually prohibited in Europe, where as it's allowed in most cases in the US.

- If you are waiting to cross an on oncoming lane of traffic and someone coming towards you flashes their lights, in the Middle East it means "wait, I'm coming", where as in the UK it means "go ahead, I'll stop".

[0] Italy is my favourite for this. People will come up behind you (doing 160km/h, while you are doing 130km/h and the limit is 110km/h :D) and start tailgating and flashing their lights until you move.

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