My best friend is a highly experienced civil engineer, specialized in designing intersections. His take on roundabouts:

- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle

- They reduce T-bone collisions

However:

- Small fender benders and sideswipes are much more frequent

- They use way more area

- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).

- Finally, they're also (mostly) worse for cyclists and pedestrians.

Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.

I live in the UK, which has roundabouts, mini roundabouts, double and triple roundabouts, traffic-light controlled roundabouts, and magic roundabouts. They work perfectly fine.

The difference is that traffic flows very differently in the UK to the US. In fact, the way traffic flows in those two countries captures a lot of their cultural differences. In the US, everything needs a grand overarching theory and imposed order, which is why Americans need traffic lights, and why they’re so keen on a very specific set of liberties that allow them to freely live such similar lifestyles. The UK embraces mild chaos and ruthless pragmatism, with everyone finding locally optimal solutions to their own problems, so things like roundabouts fit well with the national mindset.

There are more positives. - They keep traffic flowing better so you won't get "platoons" of cars all moving and stopping at the same time. This is especially effective when you do this in a sequence of intersections. - They calm do down traffic by forcing cars to slow down. - You don't need to install and maintain traffic lights.

> the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery.

Slowing/calming traffic like this is a good thing. Make it impossible to speed. Enforce the existing 35mph speed limit via concrete rather than allowing cars to rip through a yellow light at 70mph. You're also ignoring this aspect when you call roundabouts "(mostly) worse for cyclists and pedestrians".

In Sweden they have these huge roundabouts in the countryside. Very large diameter and gentle curves. You can maintain your speed. Awesome. Saves energy too. I assume there's a huge amount of tried and tested traffic innovation that could be directly just copied.

I think that's overly negative. Roundabouts have their place, mostly for low traffic intersections, but I agree that they tend to be overused, also here in Europe. Two examples where roundabouts are not the right solution:

- when there is too much traffic: if there is a constant stream of cars in the roundabout so you have to wait for a long time before being able to enter it, or force your way in (risking a fender bender), that's

- when you actually want traffic to flow. My small city has built a bypass road which is however IMHO completely botched: it starts with a roundabout, and the first exit leads to the route going through the center, only the second one goes to the bypass, so people are more likely to drive through the town. And it has three more roundabouts along the route, further making the option unattractive (in addition to a relatively low speed limit of 60 km/h and several tight curves).

As someone who drives manual, and so actually having to downshift myself when necessary, I would rather negotiate a larger roundabout 100% of the time than having to stop at a red light 30% of the time.

On my current gearbox, I can dip to around 30 km/h and gently accelerate while staying in 4th gear, which I'd be in up to around 50 km/h. So if I hit an uncontended larger roundabout that takes me 50-30-50, I don't have to do anything, transmission-wise.

Manual driving culture is probably one reason roundabouts have been popular in Europe long before North America started to warm up to them.

Roundabouts do not need more space.

You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.

As a bicyclist and pedestrian (in Denmark) what is it that’s worse about roundabouts for me? I think they work really well.

It would be interesting to know your (friend's) country of origin.

> They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).

This point is so under-appreciated. Roundabouts are really good in some cases, but they're over-utilized in England. Imagine if the US had roundabouts on the interstate and you're getting close.

I live in the US and roundabouts simply don't work.

Thank you so much for putting into words what I have feeling but struggling to verbalize. (Boston area, drive for work.)

There is one more downside, they are easy to get lost in, especially in an unfamiliar area. Apple Maps does an OK job guiding me most of the time, but just yesterday I spent an extra 25 minutes going through the same roundabout 3 times before I went the right direction, and each time I had to drive the wrong way, turn around, and then negotiate the same roundabout again.