There is no contest. Roundabouts are better than silly multi-way stops any day of the week.

There are hundreds of reasons why. But I'll just name the most obvious one that you've missed.

Traffic volume.

Multi-way stops just kill traffic throughput.

Its a hard fact. You make each vehicle stop.

Meanwhile roundabouts can safely and efficiently move staggering amounts of traffic. Want to move more traffic ? Add an extra lane or two.

P.S. As for the bicycle saftey...

Historically yes, but only to a degree, because I'd argue that if you can't manage to avoid hitting a bicycle on a roundabout then you probably should not be driving because you are most likely also committing lots of other dangerous driving offences elsewhere.

Going forward however, it should be stressed that a lot more attention is being paid to cyclist safety, both in terms of further re-enforcing driver awareness (i.e. more prominent in driver training and examination) but also in terms of vehicle design (especially HGVs) and roundabout design.

I could also argue that with a multi-way stop, perhaps especially at night or in inclement weather or where HGVs are at play, that your cyclist might not be immune to death or injury.

Multi-lane roundabouts are problematic. If you have to change lanes in a busy roundabout it can be difficult to find a gap or have someone let you over. And if you're on an "inner" lane you will clearly have to cross the outer lane at some point to get off of the roundabout. I'm not talking about roundabouts that have a special lane for people turning right, which is helpful, but roundabouts that have two or more lanes in the main circle.

> Meanwhile roundabouts can safely and efficiently move staggering amounts of traffic.

I don't find this to be accurate--at least in the US and in my limited experience in the UK. In computer terms, roundabouts don't guarantee progress under contention.

Roundabouts seem to work when there is semi-continuous, medium-level amounts of traffic. They are better than stop signs, better than unsensored signals, and probably comparable to sensored traffic signals (which are more expensive).

However, once the traffic becomes high, roundabouts are TERRIBLE. Stop signs and controlled intersections at least guarantee some progress while someone may sit at a roundabout entrance almost indefinitely since "give way to traffic on the roundabout" is the normal rule. This is particularly bad when you are entering a roundabout between the most popular inlet and the most popular outlet.

> in my limited experience in the UK

I think you need to spend a bit more time in the UK !

Take Hyde Park Corner for example. A bit of an extreme example as it is a super-busy roundabout. I will grant you that its not one where you will make smooth progress during peak rush-hour (outside of peak it works perfectly though).

There are also other good (and less extreme) examples along the secondary routes out of Heathrow (i.e. along Bath Road and Great West Road).

There's no way in hell you could replace any of the above with a US-style multi-way stop and achieve the same throughput of traffic.

Roundabouts work so well because you can have that magical combination of vehicles already established on the roundabout and also adding new vehicles all the time.

At very busy roundabouts in the UK, drivers usually yield in turn to traffic joining that in theory they have priority over.

Also at busy roundabouts in the UK it is expected that you will arrive to join the roundabout via the correct lane for the exit you desire.

If you try to join via the wrong lane then you're in for a world of hell. ;-)

Roundabouts fall apart when one road is much busier and dominates it, and nobody else can get in. Happened to me once and I was there waiting to get in for at least 5 minutes until I just forced my way in.

Roundabouts would use less gas compared to stop signs or lights. A car is going to use the most fuel when it goes from stopped to moving. A roundabout will reduce the amount of cars that have to come to a complete stop, unlike a stop sign or light where stopping is mandatory.

>In my European experience roundabouts are better for cars safety

Correct - roundabouts reduce traffic fatalities in intersections quite signficantly.

>worse for bicycle safety (cars are driven closer to bikes)

I think this probably depends on design - if cyclists have a separated path with a raised crossing, then they are likely safer than intersections.

>use up more land,

Arguably true.

>increment gas consumption (almost stop and then go vs just go). The latter point could be debated because it's worse for the cars on the main road, better for the ones on the small ones.

Roundabouts generally replace signalled intersections, and compared to those, roundabouts are probably better (slow down/yield vs full speed/full stop).

At least in the Dutch roundabouts I’ve seen that people hold up as a standard, bicycles are not supposed to take the lane but instead have a separated path along the perimeter.

I think the grandparent comment is also coming from the US, where all-way stop intersections are extremely common.

Is there a cyclist road all around the roundabout then that easy to get on and off?

Usually not. Bicycle roads are a pain if the road they run along has many intersections and roundabouts. You loose so much time and you don't have an engine to go back to speed. I usually stay on the road but I'm doing at least 25 km/h. Families or people with low saddles usually do half that speed and bike lanes are good for them.

You would probably be in the protected path separated from the road to begin with.

Reference: https://bicycledutch.wordpress.com/2013/05/09/a-modern-amste...

Yes. The Netherlands have standalone bicycle paths as the standard. Not a line on the sidewalk, not a lane on the road, but a completely separate path that is designed to avoid both pedestrians and cars.

As more roundabouts have appeared in my boring flyover city in the last decade (from ~none to quite a few) I have started wondering what it's doing to my tire balance and suspension.