Crash prone 'modern roundabouts'

[tradephoric]

FDOT is going crazy building "large complex" roundabouts along US41 through Sarasota.  The double-lane roundabout at Venice & Jacaranda Blvd is currently the most crash prone intersection in Sarasota County but the triple-lane roundabout design they are planning at Gulf Stream & US-41 should take the cake.

[jakeroot]

FDOT is going crazy building "large complex" roundabouts along US41 through Sarasota.  The double-lane roundabout at Venice & Jacaranda Blvd is currently the most crash prone intersection in Sarasota County but the triple-lane roundabout design they are planning at Gulf Stream & US-41 should take the cake.

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

[DaBigE]

FDOT is going crazy building "large complex" roundabouts along US41 through Sarasota.  The double-lane roundabout at Venice & Jacaranda Blvd is currently the most crash prone intersection in Sarasota County but the triple-lane roundabout design they are planning at Gulf Stream & US-41 should take the cake.

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

Adding an island one of the only ways to get speed control on a 3-lane approach. Without it, the fastest path measurement would basically be a straight line. It also adds another point of refuge for pedestrians.

[kphoger]

I do find it ironic that I'm defending whether or not my design is a roundabout considering how many times i have been accused of hating roundabouts or something to that effect.

If I hate Russians, then marry a Polish woman, is that ironic?

(For the record, I don't hate Russians, and my wife is part Polish.)

[tradephoric]

If I hate Russians, then marry a Polish woman, is that ironic?

(For the record, I don't hate Russians, and my wife is part Polish.)

That all depends if you colluded with the Russians to get with the Polish woman!  If so well done.

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

Another interesting thing with that Carmel roundabout design is that it has double right turn lanes coming out of the roundabout at two of the approaches.  I don't remember seeing that before.

[silverback1065]

FDOT is going crazy building "large complex" roundabouts along US41 through Sarasota.  The double-lane roundabout at Venice & Jacaranda Blvd is currently the most crash prone intersection in Sarasota County but the triple-lane roundabout design they are planning at Gulf Stream & US-41 should take the cake.

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

it's called deflection, it's necessary for large vehicles that need more room. 

[jakeroot]

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

Adding an island one of the only ways to get speed control on a 3-lane approach. Without it, the fastest path measurement would basically be a straight line. It also adds another point of refuge for pedestrians.

I see. Makes sense. If sharper entry angles were utilized, perhaps they wouldn't be necessary?

Another interesting thing with that Carmel roundabout design is that it has double right turn lanes coming out of the roundabout at two of the approaches.  I don't remember seeing that before.

Yeah, that is pretty unusual. Multi-lane roundabouts were the first widespread use of double (or even triple) lane yields, for most jurisdictions. It does not surprise me that at least one roundabout in the US implemented a double right turn with a yield. I bet there's more out there. Most double right turns at regular intersections are signalized, though there are many in Alberta that use yield signs, just like the Carmel roundabout. No idea how successful they are.

it's called deflection, it's necessary for large vehicles that need more room. 

No no, the small raised islands in between the approach lanes, not the curvature of the approach leg itself.

[silverback1065]

If you're talking about the far ones on the right side, it's an added lane so they don't really have to stop.

[jakeroot]

If you're talking about the far ones on the right side, it's an added lane so they don't really have to stop.

Look at the video at the top of the page. The right lane for the left and right approach has a small, mountable island, despite not being a slip lane. Those far-right lanes still have to yield.

DaBigE already answered my question:

Adding an island one of the only ways to get speed control on a 3-lane approach. Without it, the fastest path measurement would basically be a straight line. It also adds another point of refuge for pedestrians.

[DaBigE]

I don't understand some of these approach lane designs. Why are some lanes separated by an island, while others are not? I understand this design with a slip lane, but not for another lane that also goes straight. This roundabout in Carmel has an island for the southern approach, between two lanes that go the same place. I don't get it.

Adding an island one of the only ways to get speed control on a 3-lane approach. Without it, the fastest path measurement would basically be a straight line. It also adds another point of refuge for pedestrians.

I see. Makes sense. If sharper entry angles were utilized, perhaps they wouldn't be necessary?

Maybe. Every adjustment comes with a trade-off; it's hard to say for sure without playing around with the design and knowing the design vehicles. A more likely possibility would be to have an approach that is more chicaned rather than a simple deflection. But I'd still recommend retaining the islands, to make the approach more pedestrian-friendly. Crossing two lanes of semi-regulated traffic is bad enough. Three is insanity if the vehicular traffic is present that warrants a 3-lane approach.

[tradephoric]

2 dead after car hits boulders, catches fire in Little Rock traffic circle
https://katv.com/news/local/vehicle-catches-on-fire-after-hitting-boulder-in-little-rock-traffic-circle

Why do they have to put boulders in the central islands of these roundabouts?  Two are dead in Little Rock after their vehicle struck the boulders and caught fire.  What's so wrong with having a central island design void of fixed objects (especially outside of central business districts)?  Raised curbing in the central island would likely disable any "drunk driver" who blows through the central island but they wouldn't come to a "dead stop" by hitting a boulder.  Here's a good example of a grassy central island with a raised curb.   

https://www.google.com/maps/@44.8960769,-88.2470036,3a,75y,85.2h,85.59t/data=!3m6!1e1!3m4!1stPCaTkK119UNr9aElKmIkQ!2e0!7i13312!8i6656

[kphoger]

I think they should make the boulders out of Nerf.

[MNHighwayMan]

I think they should make the boulders out of Nerf.

Or just make them explode. Would be way cooler.

[tradephoric]

It would be interesting to see if this design would work or if the traffic volumes turning onto Berdan Ave are too high (requiring the dual circulating lanes).....

Looks like the city of Toledo will be redesigning the roundabout at Detroit, Berdan, and Cherry.  It sounds similar to the plan i had proposed over 3 years ago.  Ultimately they are reducing it from a 2x2 roundabout to a 1x2 roundabout, which is the quickest way to reduce the number of crashes occurring at these problematic roundabouts.

Changes coming to roundabout at Detroit, Berdan, and Cherry
https://www.toledoblade.com/local/transportation/2019/08/09/multilane-toledo-roundabout-modified-crash-problem-road-construction/stories/20190808124

[JCinSummerfield]

Hallelujah!  I wonder every time I go through there if someone next to me is going to turn right from the left lane.

[tradephoric]

^Yep.  The geometry of that roundabout made it such that the pavement markings were ambiguous to drivers. I'm glad they are finally fixing the problem.

[kalvado]

Hallelujah!  I wonder every time I go through there if someone next to me is going to turn right from the left lane.

But wait, this is completely legal by design, and should have minimum effect on your actions - it matters only when you enter roundabout; further down the circle right lane should exit anyway

[kphoger]

Wow, I fully expected this news article to appear in the thread...

Driver banned after dash cam footage shows van flying over a roundabout

Andy, of Hingham, Norwich said: "I was actually on my motorbike behind him so I saw it all.

"I pulled over along with some other drivers to see if he was OK.

"It is quite a bad roundabout, he just didn't see what was coming because he was going so fast.

"The driver had a few cuts and bruises but the ambulance came straight away and took him to hospital.

"He just didn't see the roundabout coming."

[MNHighwayMan]

"He just didn't see the roundabout coming."

Damn sneaky bastards. Never know when they'll jump up and overturn a truck or set a van in flight.

[ET21]

"He just didn't see the roundabout coming."

Damn sneaky bastards. Never know when they'll jump up and overturn a truck or set a van in flight.

Curse those road circles

[JCinSummerfield]

Hallelujah!  I wonder every time I go through there if someone next to me is going to turn right from the left lane.

But wait, this is completely legal by design, and should have minimum effect on your actions - it matters only when you enter roundabout; further down the circle right lane should exit anyway

When entering the mentioned roundabout from Cherry Street, the straight through movement is to Berdan Ave.  many people believe the straight through movement is to NB US-24, when in fact that is a right turn.  If I'm in the right lane trying to get to Berdan, I stand probably a 50/50 chance of the guy on my left hitting me trying to turn right.

[kalvado]

Hallelujah!  I wonder every time I go through there if someone next to me is going to turn right from the left lane.

But wait, this is completely legal by design, and should have minimum effect on your actions - it matters only when you enter roundabout; further down the circle right lane should exit anyway

When entering the mentioned roundabout from Cherry Street, the straight through movement is to Berdan Ave.  many people believe the straight through movement is to NB US-24, when in fact that is a right turn.  If I'm in the right lane trying to get to Berdan, I stand probably a 50/50 chance of the guy on my left hitting me trying to turn right.

Well, you may do two things:
1. Thank those who designed nice and conspicious pavement markings
2. Apply some defencive driving concepts, and make sure you anticipate mistakes other motorists are making by using safer lane.

Last, but not the least: apparently, signs designating right lane on Cherry side for right and straight through are not compatible with NE-bound Detroit/24 approach, where both lanes are designated as through lanes. Eliminating straight through option for right lane on Cherry and removing a second lane between two legs of NE branch may be a good idea.

[Chrispi]

Using turn signals properly in a roundabout will help immensely.  Of course, some parts of the country have an even bigger problem with signalling!

[kalvado]

Using turn signals properly in a roundabout will help immensely.  Of course, some parts of the country have an even bigger problem with signalling!

you mean turning on emergency flashes to indicate left and right turn at the same time?

[Chrispi]

Using turn signals properly in a roundabout will help immensely.  Of course, some parts of the country have an even bigger problem with signalling!

you mean turning on emergency flashes to indicate left and right turn at the same time?

Any signal would be good, for most of the morons seen on the road.