Why are roundabouts hard for some people?

[MillCreek]

Roundabouts are becoming more popular in the Puget Sound Region, and I go through at least two of them every time I drive.  Here, they are primarily put in as a cheaper alternative to a signal, and at intersections prone to T-bone collisions.

[K Frame]

We have a very interesting one near my house. It's actually a hybrid circle around straight through E-W lanes.

Hopefully this map view will work...

https://www.bing.com/maps?q=fairfax+circle&FORM=HDRSC4

There's a lot of discussion about how they're going to change that intersection because it can be a real SOB to navigate, and as traffic increases it's getting a lot worse.

[RoadKingLarry]

Trick question.  No one uses turn signals in a round-about!

What are turn signals?

[Hawkmoon]

Because they have become a new Green panacea to every stop light in creation, and are often used in places no sane Englishman would put them.  Too small a radius, too many lanes, too many entrances and exits, and conflicting signs.

I'm old enough to remember when roundabouts were considered to be unsafe and there was a concerted effort to eliminate them as much as possible.

[MechAg94]

The main downside to me is the additional land needed over just a 4-way stop.  Depends on where it is I guess. 

[Hawkmoon]

There's a lot of discussion about how they're going to change that intersection because it can be a real SOB to navigate, and as traffic increases it's getting a lot worse.

That's a rather complex variation on the "jughandle" intersection.

[K Frame]

That's a rather complex variation on the "jughandle" intersection.

My Father was a highway engineer for most of his career. He was NOT a fan of that particular intersection, but apparently it was the "in" way of dealing with that kind of intersection back in the 50s and early 60s.

[MechAg94]

Does that include an over/under pass?  If not, I don't see how that is supposed to work well.

[K Frame]

Does that include an over/under pass?  If not, I don't see how that is supposed to work well.

As it is right now? No. It's all surface streets.

For update planning? Over/under pass is one thing that's been discussed, but it's still in the discussion and proposal stage.

https://www.fairfaxva.gov/government/public-works/transportation-division/current-transportation-projects/fairfax-circle-intersection-improvements

The kicker? the area just got a LOT tighter as a big mixed use residential commercial redevelopment block is just about finished, and it sits just down from the circle on the main artery.

[MechAg94]

The worst I remember having to use a while back was a clover leaf style exit with an overpass (exit off the feeder road).  The conflict with the entrance ahead of the exit just didn't work at all.   Only took a small amount of traffic to bog it down. 

https://www.google.com/maps/@29.5403391,-95.1418132,409m/data=!3m1!1e3
They completely rebuilt it a few years back into a massive stop light and underpass.  The old cloverleaf roads seem to still be there as a remnant.  I think the number of people in that area has increased a lot over the last 30 years.  I moved out of that area 15 years ago.  Just bad memories of that intersection.

[K Frame]

Cloverleafs were a great concept when the interstate system was designed...

But traffic levels in a lot of areas grew at far greater rates than planners ever anticipated.

And, as you point out, the failing in the design is driven by the amount of converging traffic.

Cloverleafs were generally picked as the primary interstate intersection because the could be meshed fairly well with surface streets or other interstate-style roads. They could also be pretty much cookie-cuttered in a lot of situations without a ton of redesign.

They take up a ton of land compared to other kinds of intersections but that wasn't as much of a consideration in the 1950s and 1960s when interstates were being built.

[MechAg94]

https://www.google.com/maps/@29.4947059,-95.0375602,243m/data=!3m1!1e3
Dredging up memories.  This is Clear Creek Gun Range which I shot at a number of times when I lived in that area.  I think it only went to 200 yards.  There was not a subdivision just down range when I was there.  Someone told me they had added barriers in front of the shooting benches so you couldn't elevate your muzzle above the berm.

[Fly320s]

That is an educational graphic, but how does a driver who is unfamiliar with the intersection know if it is a round-about or traffic circle?

[TechMan]

One of the high traffic State routes has multiple Superstreet intersections.

https://www.youtube.com/watch?v=_3-lLBZbRqo

[Ron]

That is an educational graphic, but how does a driver who is unfamiliar with the intersection know if it is a round-about or traffic circle?

For roundabouts, I believe you will see signs similar to expressway signs letting you know the proper lane to be in for your destination.

Having been in Illinois most of my life my experience with both is a bit limited.

[Larry Ashcraft]

Cloverleafs were a great concept when the interstate system was designed...

But traffic levels in a lot of areas grew at far greater rates than planners ever anticipated.

And, as you point out, the failing in the design is driven by the amount of converging traffic.

Cloverleafs were generally picked as the primary interstate intersection because the could be meshed fairly well with surface streets or other interstate-style roads. They could also be pretty much cookie-cuttered in a lot of situations without a ton of redesign.

They take up a ton of land compared to other kinds of intersections but that wasn't as much of a consideration in the 1950s and 1960s when interstates were being built.

The "mousetrap" in Denver comes to mind.   It's where I-25 and I-70 converge.  It's an absolute nightmare, despite having been revamped several times since the sixties.  But if you MUST get to I-70 from I-25, there are other ways to go.  Hwy 225 works, but the easiest way is E470, which is a toll road.   As to roundabouts, there are a bunch in Centennial  (SE suburb of Denver), where my youngest daughter lives.  They are mostly where three roads intersect.  We there last week, and didn't have a lot of trouble with them.

[K Frame]

One of of the weirdest experience of my life involved a traffic circle...

I was driving back to DC from Iowa not long after I moved to DC. We'd started out in Davenport, Iowa (4 of us went to another friend's wedding) at probably 5 in the morning. By the time I got my car at my parent's house in Pennsylvania it was nearly 11 at night and I still had 2 hours to drive. I was freaking exhausted...

I got onto the Chevy Chase Circle.... and I couldn't find my way off of it. I don't know how many times I went around that damned circle... Somehow I finally found the correct street (seemed like hours), got to my apartment, and absolutely collapsed.

[Fly320s]

Big Ben!  Parliament!

[MechAg94]

One of the high traffic State routes has multiple Superstreet intersections.

https://www.youtube.com/watch?v=_3-lLBZbRqo

That looks like it is designed to obstruct traffic and confuse drivers. 

[TechMan]

That looks like it is designed to obstruct traffic and confuse drivers.

The major route has the the regular flow of traffic and the cross streets have the odd flow.  It looks odd, but I've driven through it and it does work.

[K Frame]

I think they installed on of those Superstreet intersections on I-66 west of DC... Only I seem to recall it being a counterflow superstreet or something like that.

Nope, I think it was actually a diverging diamond...

[K Frame]

Wow! I just found a really neat page on the Virginia Department of Transportation website...

It's a listing of all of the various intersection types and their benefits and drawbacks...

http://www.virginiadot.org/innovativeintersections/default.asp

[Hawkmoon]

The text says a roundabout has the lanes striped as a spiral.

The one in the illustration doesn't. I fail to see any significant difference between the two.

[Angel Eyes]

https://www.youtube.com/watch?v=cPCLFtxpadE

 

[bedlamite]

https://youtu.be/6gVWVagKTSo?t=12