Roundabouts lock up if the major flow of traffic has to go 270 degrees. (A left turn in an RHD country)
Diverging diamonds do their best at handling large left turn flows since that is the type of movement that has the most reduced number of conflicts. To get any lower you would need to start building flyover ramps.
I think it depends on the specific traffic expectations, a roundabout interrupts the traffic flow of everything that feeds into it... the double diamond can prioritize a more uneven flow in one direction (so might be better in cases where lots of people travel in one direction, like rush hour)
Might also be worth mentioning that Americans seem to be really bad at using roundabouts because they're not common in much of the country.
Having said that, as someone who has some historical familiarity with these sorts of intersections, but doesn't live in a country that has them, they are pretty scary too when encountering them only rarely.
I live in a Canadian province that has enthusiastically embraced roundabouts, so I’ve been able to get used to them for years. Their efficiency is very dependent on drivers being able to anticipate the actions of others.
These are things like watching the angle of the front wheels, the speed at which other cars are taking the intersection (faster = going straight through; slower = taking the turn), but also how much time it takes for a stopped car to start moving so you can judge whether you have time to enter the intersection.
This is a learned skill, and not everyone in the general population has the cognitive capacity to reliably pick up on these cues.
I’m not saying that I’m Nigel Mansell, but I genuinely think that the inability to pick up on these cues is why many are terrified and opposed to them.
For context, that's a very specific kind of roundabout that you find near the junction of a motorway (the M1) with a primary road (the A630). The roundabout is situated on the A-road and accessed from the motorway by a slip road. That way, motorway users who don't care about the junction can just keep cruising forwards and drive over the top of the roundabout. Nevertheless, drivers can approach from any direction and exit in any direction (including back the way they came). It doesn't look like this is the case in OP's article; I'm not sure how someone approaching from the left can continue in the same direction and drive off to the right.
Where I am in the US, you run into them a lot. I find them easy to deal with, but I learned to drive on them.
But it is funny watching non-locals deal with them and I can see why they dislike them. They work great when only people use to them drive through them.
Are you afraid of the inner lanes? Drive exclusively on the outer one, nobody cares. Do you need to go slower because you are in doubt? No problem, take even a second turn around if you need to get extra-sure.
I need to go through 16 roundabouts everyday, and after the 1000th (2 months) you gain familiarity enough.
No. The entire point of these is to funnel the traffic onto and off the highway with out crossing any oncoming traffic, and to reduce the total number of traffic crossings overall.
bobthepanda|1 year ago
Roundabouts lock up if the major flow of traffic has to go 270 degrees. (A left turn in an RHD country)
Diverging diamonds do their best at handling large left turn flows since that is the type of movement that has the most reduced number of conflicts. To get any lower you would need to start building flyover ramps.
micromacrofoot|1 year ago
Might also be worth mentioning that Americans seem to be really bad at using roundabouts because they're not common in much of the country.
nolist_policy|1 year ago
[1] https://maps.app.goo.gl/fSzgiWabGtwFhh4b8?g_st=ac
PaulDavisThe1st|1 year ago
https://i2-prod.examinerlive.co.uk/news/local-news/article24...
Having said that, as someone who has some historical familiarity with these sorts of intersections, but doesn't live in a country that has them, they are pretty scary too when encountering them only rarely.
xattt|1 year ago
These are things like watching the angle of the front wheels, the speed at which other cars are taking the intersection (faster = going straight through; slower = taking the turn), but also how much time it takes for a stopped car to start moving so you can judge whether you have time to enter the intersection.
This is a learned skill, and not everyone in the general population has the cognitive capacity to reliably pick up on these cues.
I’m not saying that I’m Nigel Mansell, but I genuinely think that the inability to pick up on these cues is why many are terrified and opposed to them.
n4r9|1 year ago
Roundabouts generally look more like this in the UK (without any overpassing roads): https://www.google.com/maps/place/Howarth+Ln,+Rotherham/@53....
jmclnx|1 year ago
But it is funny watching non-locals deal with them and I can see why they dislike them. They work great when only people use to them drive through them.
otherme123|1 year ago
Are you afraid of the inner lanes? Drive exclusively on the outer one, nobody cares. Do you need to go slower because you are in doubt? No problem, take even a second turn around if you need to get extra-sure.
I need to go through 16 roundabouts everyday, and after the 1000th (2 months) you gain familiarity enough.
What is this bullshit? https://www.google.com/maps/place/Madrid/@40.4965508,-3.6484... . That monstrosity, that you need to use carefully until you memorize it, is probably unique with all the mental toll that means. First time I used it, I made a bet on a lane and prayed that it went to where I wanted. A few kilometers south of that, you have this sane roundabout: https://www.google.com/maps/place/Madrid/@40.4297331,-3.5975..., doing the same 4-way joining in a more transparent and forgiving way.
sorahn|1 year ago
Here’s a YouTube video that does a much better job of highlighting these benefits. https://youtu.be/A0sM6xVAY-A?si=qrk2ZFFYPA2-6rAS
mattlondon|1 year ago