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Comment by JoeAltmaier | Hacker News Reader

Overhead view is complex, sure. The only view that matters is thru the windshield. If the driver knows at every point where to go next, then it works fine. All about signage and lanes and signals.

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I used to agree. But people are creatures of habits. There is a well-known "large" roundabout near Copenhagen often called the IKEA roundabout. Obviously next to IKEA but still so known that it has a "popular" name. It has large overhead signs. On road signage. Traffic and street lights. The overhead signs show that you should take the left most lane to go left. Two middle lanes for straight ahead. And a breakout lane to the right which goes right. It is all very easy to understand and logical. But the number of lanes and the fact it is so busy it is regulated with traffic lights makes people very uncomfortable. As I find it very logical and easy to navigate I have come to my own conclusion that it is because this type of roundabout is unusual and uncommon around here. You will notice peoples lizard brain set in. They are scared they cannot exit so they clearly choose the outer-most of the 2 straight ahead lanes. And dangerous situations when people who needs to go left take the outer lane because you can "always" do that in a roundabout (but not here!). And for further anecdotal evidence this has come up several times in conversations and people have stated they do not like it.

You can see it here: https://maps.app.goo.gl/jr39hNie4d9fennq7

We have a similar roundabout in Dublin although it is not well signposted. People do two things that they seem to think will make them safe. First as you say they stick always in the outer two lanes. Second they increase their speed... I think on the basis that if they get through it quickly there is less chance of something going wrong.

Large busy overhead signs are not as helpful as simple arrows at each opportunity to turn. Maybe arrows on the pavement, just in front of the turn.

Our first roundabout around here had 13 (thirteen!) signs just before you entered, including a map. Disaster. Folks just want to know, which is the left-turn lane etc.

Btw is that the right link? It looks like an ordinary roundabout with right-turn ramps.

The link is correct.

The simple arrows you prefer are there as well. But the overhead signs are important when there is a lot of traffic as you will see the road markings too late.

You have to look at the satellite image to see the unusual (around here) parts: Traffic lights, stopping lines inside the roundabout and the left turn lane within.

Indeed. In fact, one could argue that a roundabout itself adds no complexity to the rules of the road. A roundabout can be understood simply as a one-way road that has priority over traffic which is joining it, which must give way (="yield" [en_US]) to vehicles already on it.

The fact that this one-way road eventually goes full-circle and connects back onto itself is inconsequential.

Yes, and even a larger multilane roundabout is just a short stretch of highway that curves round and has a sequence of normal on and off ramps along it. Even the signalling you’re supposed to do is basically exactly what you’d do if you were joining a highway then exiting again.

If the turns are labelled, ON THE ROUNDABOUT!

Our local traffic engineer doesn't label the exits. So people STOP and look around, wondering if this is their exit.

There's one roundabout between me and Boston that gets very congested at rush hour and I commuted into on and off for about 18 months. It was obvious when school started up because the backups got way worse--partially more cars I assume but presumably you also had a lot of people who just weren't used to the traffic patterns. It tended to get better (though still awful) again after a few weeks.

ADDED: (One) problem with Route 2 is that it's an arterial highway that was never designed to be one. Especially to the west, the merges are also terrible at peak times. And (although there was one major upgrade a number of years back) it passes through some of Boston's tonier suburbs which makes major changes hard.

Roundabouts are extremely sensitive to rates of traffic. If one direction occasionally fills from e.g. a school parking lot, the others can become instantly congested.

You can use traffic lights etc to fix this. But then the major benefit of roundabouts is extinguished: their cheap cost. Just some pavement and acres, painted lines.

They're great for low traffic neighborhoods where the intersections don't warrant something as heavy weight as stoplights or 4-way stops. I'd love to replace every ridiculous 4-way stop in my neighborhood with a roundabout, it would probably double the life of my brake pads and have no effect on safety. Except Americans are baffled by them and they'd probably get shouted down at the next city council meeting for being weird and confusing.

I have thought that a "zipper merge" (let one car in ahead of you) convention would help congested roundabouts but that isn't how we're taught to use them.

I'm not sure how that would work. Now the person entering the rotary has to trust that another driver isn't going to cut them off. I can tell you that merges right after a traffic light it is absolutely routine for a car (or probably more likely a pickup) not to let you alternate. I don't even bother with the FU horn any longer.

When I moved to Boston I was supersized that people would talk in fear of all the newfangled "rotaries" as they are called here. Roundabouts in general are awesome but Boston has some unique challenges.

Roundabouts work well when there is similar amounts of traffic coming from all directions. In Boston they built some roundabouts where arterial roads meet suburban streets (or country lanes) at odd angles and it causes congestion. There really isn't a great solution for those intersections though - lights would reduce traffic flow.

It's basically the Route 2-related rotaries. The Concord rotary and the "twin doughnuts of death" as you enter Cambridge. Of course, all those intersections would be nightmares at rush hour however they were designed/configured.

It also doesn't help that someone is adding visual complexity to the picture by the dim duplicate extensions on the side (what is that called?). There may be times where that feature is useful, but this is definitely not one of those times.

As long as you aren't a cyclist, that is. Separated bike lanes? Never heard of 'em...

From memory the entire thing is ringed by a cycle loop on the pavement, no reason to get out and in to traffic.

From looking at it on street view it appears to be a narrow (if paved) sidewalk that's shared with pedestrians, and the only way to cross traffic is to trigger multiple traffic lights (per crossing!) to halt traffic so that cyclists and pedestrians can safely cross, and resorting to traffic lights means that you've given up on any traffic benefits of a roundabout in the first place.

To any budding civil engineers out there, please only consider roundabouts in the following circumstances:

1. Traffic is light enough that the roundabout can be a single lane. No multi-lane roundabouts in populated areas with pedestrian crossings!

2. Traffic is remote enough that there are no pedestrians or cyclists to worry about, in which case, feel free to go crazy with your multi-lane roundabouts.

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