I'm near Carmel too. I remember when the roundabouts started going in. They replaced four-way stops that backed up for miles at rush hour. The roundabouts made traffic flow SO much better.

Now Carmel is replacing some stoplights with roundabouts. This man's opinion is that they are not always better. But so far, they've never been worse.

They absolutely suck when a train of cars forms and you can't enter the loop. Those are the dumbest roundabouts in the country. They don't adequately force cars to slow down enough to let gaps develop in the flow.

I'm not sure that slowing the cars down would help more. Its much easier to drive literally right behind a car at a slower speed than a higher speed.

Afaik, the general trend is to put a stoplight going into the roundabout for the few directions that cause a problem so that the "side streets" get a chance to go.

The other stupid thing about Carmel roundabouts is where they put them at every 3rd road crossing when it would have worked absolutely fine just to have the traffic going one way stop, because it's a neighborhood with thoroughfares and cross streets, and there is NEVER traffic on the cross streets.

It just makes the thoroughfares slower for no clear reason.

A failing activity I've seen with roundabouts is when there is no physical barrier but instead just a bump in the road that everyone is supposed to go around. In those cases, a LOT of people end up treating the round about like a 4 way intersection with the worst of all world (because you don't know if someone is going to go against the roundabout rules to turn left).

There HAS to be a lump big enough to cause someone to go the right way around.

Ours typically have a bit in the middle that's usually grass behind a curb, then a lower raised bit with a bevelled curb that's all concrete surrounding that, or else just an area around the center-grassy-bit that's even with the rest of the pavement but marked off with "don't drive here" stripes. The ordinary lanes are outside both.

I assume those are affordances so buses (say, school buses), trucks towing trailers, and stuff like that, can actually use the roundabouts. They'd be damn tricky for them to navigate, otherwise.

Kinda off topic, but this reminds me of a racing game I played which had a track that featured a roundabout with a bump just perfect for Dukes of Hazarding it.

So ideally the roundabout also doesn't encourage sweet jumps. (Unless there's a very well-designed designated landing spot that prevents damage to the vehicle. Probably tax dollars can be spent on better things.)

What if they put a flexible bollard in the center?

All anecdotal but hey: The roundabouts I've seen fail (we have many) are those with not enough and too much obstruction. The versions with some form of gradual grace (curved edges around a center platform or lots of grass and a bump) tend to work best. One of the worst ones was a very large one with a meter high round wall as center barrier which caused lots of damage to those who made a mistake. The too small ones are just intersections with minor obstacles to navigate.

Tall stuff impedes vision. The gental slope around tends to be accommodating for tractor trailers. Short stuff, even just a regular curb inside of the sloped area should be enough to stop cars from driving through it. Some short flowers or plants can help draw attention.

You want to impede vision across so people focus on what is important for their merge.

That's only potentially true with very large circles. Small round abouts are so small that you want to be able to see obstacles before you even get to the point of preparing merging.

> I live near Carmel, Indiana, the roundabout capital of the US. Small ones, large ones, figure 8's, figure... double-peanut-looking things with elevated crossovers near interstate junctions. They work well and keep traffic moving. But there is a learning curve. Every new roundabout causes a significant jump in crashes for a short time. Though, those crashes tend to be "glancing blows" that cause less serious injuries due to the angle of attack imposes by the roundabout.

I have a reason to visit Indiana now! Cool. I wonder how I can sell the family on a trip to Carmel or similar city :).

The town I grew up started adopting roundabouts as I started driving. They're awesome and so much faster than red lights! They annoy my older relatives and coworkers as well.

Carmel is basically a suburb of Indianapolis, and all kinds of things happen at the Indianapolis Convention Center. Surely you can sell your family on one of them!

Recent video where roundabouts in Carmel are a big focus, from pedestrian/cyclist POV: https://www.youtube.com/watch?v=rqx6aRCO0MI