My city has a lot of roundabouts, some are quite big (~150m diameter) as they are used where two or more main roads meet.

When I first came here they usually had three lanes, with the idea that you change lanes as you move through the roundabout - this meant almost daily you would see a minor RTI on a roundabout, which would cause large queues of traffic. Some roundabouts also had three lanes where you enter and exit, but they were usually signalled.

A few years ago they reduced the roundabouts to two lanes, and all exits to one lane. The idea being that for the first and second exit you need to use the outer lane, and for the third or fourth exit you use the inner lane. That inner lane becomes the outer lane after the second exit, so you just stick to the same lane once on the roundabout. The only time you need to change lanes is if you miss your exit and need to go around again. There are clear signs before you reach the roundabout saying which lane you need for which exit.

Since this change was made, I think I've seen maybe one RTI on a roundabout - when somebody was being stupid and tried to overtake a bus. It's such a simple change, but it's crazy how effective it has been. They've also started adding speed bumps to some roundabouts to slow traffic, which actually increases capacity as it's easier to join with slow moving traffic.

They put two roundabouts in here on a state highway. I've never talked to anyone who had good things to say about them.

The main problems IMO are:

- you can just go around again if you aren't sure which exit you need; you are forced into taking an exit, right or wrong

- the radius is too small so there is not much time to make a complex decision, especially if you aren't already familiar with the exits

- it's hard to monitor traffic entering the roundabout to make sure I don't get hit by someone having a harder time navigating this than me, while at the same time trying to figure out what the crazy sign diagrams mean.

- there's no confirmation when you do take an exit that you've taken the right one. Might not be a road sign for 10-15 seconds, which is a long time when you're not sure where you're going.

- they're even worse at night because there's not enough lighting. Not too bad for the exits toward civilization, but pretty confusing for the more rustic ones.

I think the idea is okay, but at least for the ones they put in here, the execution is not so hot.

Had to remind myself of the difference between a roundabout and a traffic circle, suspecting some local mislabeling. From https://www.ofallon.org/street-division/faq/what-is-the-diff... :

> Roundabouts are not traffic circles. Roundabouts follow a yield at entry rule, which requires approaching vehicles to wait for a gap in the circulating traffic before entering the roundabout. Roundabouts involve low speeds for traffic entering and driving through the roundabout; they use deflection to slow entering traffic and enhance safety. Vehicles in the roundabout have the right of way.

> Another distinguishing difference between traffic circles and roundabouts is that roundabouts have a smaller diameter than most traffic circles, resulting in safer conditions and lower speeds. Vehicles can enter modern roundabouts much easier than traffic circles due to flared approaches, entry angles, slower speeds on the circulating roadway and the fact that vehicles entering roundabouts always yield to circulating traffic.

> Entering a roundabout is as easy as making a right hand turn onto a one-way street.

I've driven through an intersection almost daily my entire life. It was switched to a roundabout a few years ago. I have had more near misses in that roundabout from people not yielding or people continuing around in the outside lane than my entire life driving and never had a single issue with the intersection prior to it being a roundabout. I like roundabouts. I would like to see a study on how many near misses happen in roundabout vs. regular intersections. Too much stress.

Not sure if this is also the case with roundabouts, but traffic circles are significantly more hazardous for cyclists than intersections.

https://cyclingincities-spph.sites.olt.ubc.ca/files/2018/06/...

For sure, though "it depends" comes into play. Roundabouts down scale well beyond 3 lanes and if one gets clogged up it can have a butterfly effect that causes clog ups at other intersections

At least with a standard crossing intersection of say the E->W road is hosed up because of a traffic accident the other flows of traffic are unaffected as long as the intersection remains clear. Even if some jerk gets stuck in the middle they have the ability to U turn out to unblock the intersection.

With a roundabout when it's not clogged its very nice and I do enjoy them. But I've also been stuck at an intersection for more than an hour because of a fender bender in a roundabout causing a full traffic stoppage with no way out.

Phoenix area added a bunch of roundabouts a while ago and last I heard they were in the process of taking them out.

Problem is if people are used to them they work well but if you rarely see them people don’t really understand the concept and just kind of blast through them without yielding.

Almost got taken out a few times when I was a cabbie, people just go full speed into them without looking.

The new hotness seems to be intersections where the traffic crosses over to the other side and left turns are uncontested(?).

I don't really enjoy roundabouts, but I like the idea of a non-blocking (or less-blocking) traffic network.

Head-of-line blocking, where left turns can block through traffic or through traffic can block a left turn lane, is a particularly irritating feature of traditional intersections.

I live in Massachusetts, the land of the rotary. Rotaries here are amazing with multiple lanes of crossing traffic, traffic lights, and occasionally making traffic IN the rotary yield to entering traffic.

My favorite is Newton Corner, 3-4 lanes of chaos in a 1/2 mile circumference featuring 200+ street signs, 23 crosswalks, 12 traffic lights, intersecting 6 local roads, and a highway interchange. Oh, there's also a couple bus stops for the 10 or so bus routes. One is generally required to cross several lanes of traffic to exit the rotary at the desired location.

The roundabouts that have popped up are downright relaxing in comparison.

I drive through Carmel frequently and love the efficiency of their roundabouts. Anecdotally, I haven't had significant issues with other drivers not using them effectively. Meanwhile in Indianapolis, I often find myself stopped at a stoplight with no cross traffic, wishing that we would invest more in roundabouts like Carmel has. Granted, Indy is much larger, older, and more dense than Carmel, but there are still plenty of locations where roundabouts would be a good fit.

Roundabouts are an amazing alternative to stop signs and red lights, especially in busy streets of medium/small cities.

Rotaries on the other hand are super-confusing and an aberration in the history of traffic management.

They reduce car on car accidents, but sadly increase car on bicycle accidents as many car drivers fail to yield to the cyclists that are circling, especially when exiting the roundabout.

* Except in the rest of the United States.

I have long suspected that what makes roundabouts safe is that they feel like they aren’t. People speed when the lanes are wide as well. There have been some people experimenting with optical illusions that make highways feel less safe than they actually are, such as forced perspective to make obstacles off the highway look closer, which encourages the drivers to slow down and pay attention.