US and the roundabout

[bothar]

There is an article in the Times today about US roundabouts, this seems to be a synopsis of the data in the Washington Post article below, this seems to allow one view without logging in
https://www.washingtonpost.com/business ... c-circles/

It notes the steady growth in roundabouts to 9000+ in the US, which is still rather few. Carmel, Indiana seems to be roundabout HQ.

[Gav]

https://goo.gl/maps/GRyUsWYRK4g9YUqq6

very similar to a typical roundabout over a dual carriageway - its similar but going round it on google earth feels diferent.

There are loads of roundabouts in the boston area. but all may appear as roundabouts and sort of function as a roundabout but they look so different, with signage and markings being so different and strange.

no real signage no real understanding of the ins and outs....

[Gav]

https://goo.gl/maps/DLw9Lc92etfpNrfX7

I-95 over pass. roundabout interchange

[wallmeerkat]

https://goo.gl/maps/DLw9Lc92etfpNrfX7

I-95 over pass. roundabout interchange

Strange how this one feels more like traffic merges rather than stops (if needed) at the roundabout, the lack of lines compared to the over-complicated roundabouts here is refreshingly old fashioned.

[KeithW]

Strange how this one feels more like traffic merges rather than stops (if needed) at the roundabout, the lack of lines compared to the over-complicated roundabouts here is refreshingly old fashioned.

As I recall they use Yield (Give Way) signs in Massachussets and use specific signs for the classes of traffic banned on the Interstate - ah yes here it is.
https://www.google.com/maps/@42.4992681 ... 384!8i8192

In Ohio you are halfway down the sliproad before you see the sign.
https://www.google.com/maps/@40.0863931 ... 384!8i8192

[Chris5156]

https://goo.gl/maps/DLw9Lc92etfpNrfX7

I-95 over pass. roundabout interchange

Strange how this one feels more like traffic merges rather than stops (if needed) at the roundabout, the lack of lines compared to the over-complicated roundabouts here is refreshingly old fashioned.

These are rotaries, not roundabouts. A roundabout has priority rules and is designed so the geometry slows approaching traffic. Rotaries tend to be larger, and expected to free-flow, so traffic approaches at speed and attempts to merge. They’re peculiar to the northeastern US and many are being removed or converted to roundabouts.

[Gav]

https://goo.gl/maps/DLw9Lc92etfpNrfX7

I-95 over pass. roundabout interchange

Strange how this one feels more like traffic merges rather than stops (if needed) at the roundabout, the lack of lines compared to the over-complicated roundabouts here is refreshingly old fashioned.

These are rotaries, not roundabouts. A roundabout has priority rules and is designed so the geometry slows approaching traffic. Rotaries tend to be larger, and expected to free-flow, so traffic approaches at speed and attempts to merge. They’re peculiar to the northeastern US and many are being removed or converted to roundabouts.

Not at this one... its being run as a roundabout with entry yield signs

https://goo.gl/maps/i6FsnQ7YHQtrDfpr8

https://goo.gl/maps/EVSUsBwCP5V5vg4UA

[Vierwielen]

The 4-way stop is common in South Africa - here for example. When I lived nearby, that intersection was single carriageway in each direction. This is an ideal candidate for a roundabout - there is plenty of land and the roundabout would certainly slow traffic down without forcing it to come to a complete halt. In addition, given the high rate of car jackings, coming to a complete halt in South Africa is not always sensible.

[Chris5156]

These are rotaries, not roundabouts. A roundabout has priority rules and is designed so the geometry slows approaching traffic. Rotaries tend to be larger, and expected to free-flow, so traffic approaches at speed and attempts to merge. They’re peculiar to the northeastern US and many are being removed or converted to roundabouts.

Not at this one... its being run as a roundabout with entry yield signs

I refer you to the phrase "converted to roundabouts"

Rotaries work well enough in light traffic with freeflowing conditions, but because they don't have the roundabout priority rule, they are prone to locking up under heavy traffic loads, since the concept of giving priority to traffic on the circulatory carriageway serves to ensure people already on the junction can always get to their exit. As a result rotaries enjoyed a brief heyday in the 1950s and 60s, but in more recent years many of them have either been removed or they've had roundabout priority rules added to them, like in your example. You can see that the geometry was never designed for approaching traffic to give way.

[freebrickproductions]

They've slowly been cropping-up across Alabama, especially in the northern part of the state. One of the newest ones in my area went in here, just outside of Huntsville, sometime within the past few years, replacing a traffic light. Seems there might still need to be some general education done though, as a local news reporter recording a segment on that new traffic circle caught a driver in the background, coming out of the neighborhood there, and carefully turning left onto the traffic circle and going out of it the wrong way...

On the other side of Huntsville, out closer to Madison, is this multi-lane-ish one, which is certainly signed as a multi-lane roundabout, though seems to be more designed as a single-lane roundabout with dedicated slip roads (and signed as a multi-lane one). Most roundabouts around here are single-lane ones, however, which I suppose makes sense. When I was driving cross-country last summer, I did encounter some dumbbell and dogbone interchanges on I-90, including multi-lane ones, such as this one. None of those have cropped-up here in Alabama, as far as I'm aware. Wouldn't be too surprised if ALDOT either doesn't want to deal with the cost of them, or thinks they'd be too advanced for the average driver around here. There was also this one in the Seattle area, which I suppose qualifies as something of a half-dogbone?

Also came across this fresh, multi-lane dogbone on I-65 in Crown Point, IN last summer as well. A couple of other traffic circles, at least one of which is multi-lane, exist just east of it as well.

[freebrickproductions]

A new interchange recently opened near me over in Decatur, AL, at AL 20 and Bibb Garrett Road. This interchange features a pair of roundabouts at it, though otherwise seems to be a fairly standard ParClo or RIRO interchange. Here's a news article a local station did about it:
https://whnt.com/news/decatur/new-highw ... ne-county/

Despite the interchange not "officially" being open until the following day, the road closed signs and barricades were all removed by the time I went through on the evening of June 1st, so I decided to record a quick drive through on my dashcam that evening. (Also because I straight-up didn't know it wasn't :officially" open yet, lol.)

[Bryn666]

Is the square roundabout sign in MUTCD or unique to Alabama?

As a regulatory sign it looks like it functions almost identically to our mini-roundabout sign (not used at full size ones).

[KeithW]

Rotaries work well enough in light traffic with freeflowing conditions, but because they don't have the roundabout priority rule, they are prone to locking up under heavy traffic loads, since the concept of giving priority to traffic on the circulatory carriageway serves to ensure people already on the junction can always get to their exit. As a result rotaries enjoyed a brief heyday in the 1950s and 60s, but in more recent years many of them have either been removed or they've had roundabout priority rules added to them, like in your example. You can see that the geometry was never designed for approaching traffic to give way.

Life does get complex, if you were heading to Cape Cod you had to negotiate what was called the Sagamore Rotary but it was actually a roundabout.


The people in the area handled it fine but a lot of tourists from out if state struggled.

The Bourne Rotary is still there complete with Yield signs.
https://www.google.com/maps/@41.7424934 ... &entry=ttu

[freebrickproductions]

Is the square roundabout sign in MUTCD or unique to Alabama?

As a regulatory sign it looks like it functions almost identically to our mini-roundabout sign (not used at full size ones).

It's in the MUTCD as R6-5P under Chapter 2B.


Per the MUTCD regulations, it appears to basically be our equivalent to a mini-roundabout sign. However, they do allow it to be installed at a full-sized one if the agency in charge chooses to do so.

Section 2B.44 Roundabout Circulation Plaque (R6-5P)
Guidance:
01 Where the central island of a roundabout does not provide a reasonable place to install a sign, Roundabout Circulation (R6-5P) plaques (see Figure 2B-20) should be placed below the YIELD signs on each approach.

Option:
02 At roundabouts where Roundabout Directional Arrow signs and/or ONE WAY signs have been installed in the central island, Roundabout Circulation plaques may be placed below the YIELD signs on approaches to roundabouts to supplement the central island signs.

03 The Roundabout Circulation plaque may be used at any type of circular intersection.

Although Alabama has adopted the national MUTCD, this state does have its own supplement to it as well in use, so I wouldn't be too surprised to find-out that Alabama's supplement makes the option a requirement, at least for single-lane ones, don't think I've seen many around here without one. A pair of examples locally I can think of off the top of my head, for reference: 1, 2
There are a few roundabouts around here without the plaques, though one's a multi-lane-ish one, another was more recently done by Madison County (and thus, don't believe had any federal or state-level funding held over it to ensure full compliance with the state's MUTCD supplement), and two more are on private property. One is at UAH's campus, which features Keep Right signage instead, though I believe this one may be the oldest one in Huntsville as well. The other privately-owned one is at the former site of The Mall and features some very non-standard signage at it, including a stop sign on one approach and nothing on the opposite one. Of course, this was, again, one of the oldest in the city, as it was put-in to showcase The Mall's fountain's sculpture, though I know at least some of the non-compliant signage was added in the mid-2010s.

[Bryn666]

Thanks for clarifying - I have been saying for a while that American roundabout design is making our efforts look terrible in comparison, the entry alignments and lane markings are much neater in the states. The only let down is the direction sign design at many; this needs a bit more work in my view but I find in general away from freeways that American direction signage is very poor.

[freebrickproductions]

Dunno why I only just recently remembered this, but a few years back, the intersection of AL 79 and AL 160 in Cleveland, AL, was turned into a roundabout, having been a 4-way, traffic-signal controlled intersection previously. As it's the intersection of two state routes, it appears that ALDOT felt it was appropriate to use these guide signs on the approaches, which honestly look quite nice. Turns-out it is indeed in the MUTCD as D1-5.

[bothar]

Turbo roundabout in Silicon Valley not entirely successful.

https://www.sfgate.com/bayarea/article/ ... 404019.php

[Peter Freeman]

A few years ago I was delighted to see the US adopting proper ('Modern' as they have it) roundabouts. What's more, all of their early ones were in appropriate places (low-speed local traffic), of the appropriate dimensions (small-ish, often single lane entry, exit and circulatory), and well-designed and marked. These were mainly in the western states (esp. Kansas/Mo). Now (including in the last few posts of this thread), I'm seeing less-pleasing examples.

One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.

One (I55 in Memphis) that Bryn recently noticed is far too small for the task it is taking on: roadworks (underway now) will fix I55 problem, but the roundabout outcome is predictable. Some others I've seen are just too big (the usual UK problem). USA, if you're not careful you'll fall into the same trap as UK, ending up with unfixable creations with multiple sets of traffic signals.

Carmel is special of course. The Mayor is a confessed RBT-o-phile. Most of their implementations are really good, especially the paintwork. Might be time to stop now though!

[Truvelo]

One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space).

Is that the one with the part built stubs for a route branching off US1 that was never built.

[Chris5156]

One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.

A lot of the very large roundabout-type junctions in New England - Massachusetts especially - are not part of the "modern roundabout" rollout in the US but come from the 1960s fad for "rotaries", which had no priority rules and were treated as fast-moving circular roadways with traffic merging as though on a freeway. Most are now converted to roundabout-type priority rules but their very large size and smooth geometry works against them.