what is the name of this type of roadway barrier?

April 24, 2022 3:50 PM

You come to a four-way intersection, but there is a barrier. Both streets are two-way. There is an elevated, planted barrier that compels traffic to turn on both sides of the barrier.

An aerial view would show two 90 degree roadway curves with a dividing barrier separating them. So if you are going North you must turn East from one side of the barrier. From the other side of the barrier if you are going South, then you must turn West. Images below are from the same side of the barrier.
view #1
view #2
I'm pretty sure this is called a "turn"-something, but cannot find it on Google. There are several of these in my residential neighborhood in Oakland, CA.
Anyone?

posted by sugarbx19 to Grab Bag (14 answers total)

Is this different from a traffic circle?
posted by BrashTech at 3:58 PM on April 24, 2022

Best answer: Berkeley calls this a diagonal traffic diverter.
posted by migurski at 4:07 PM on April 24, 2022 [7 favorites]

Diagonal diverters? They seem to be more of a West Coast thing.
posted by geoff. at 4:17 PM on April 24, 2022

I would just call it two roads that go really close to each other.
posted by Hatashran at 4:31 PM on April 24, 2022

Could you post the location of one so we can view it on Google Maps? Having trouble grasping the geometry of the intersection from the images you posted.
posted by dusty potato at 4:48 PM on April 24, 2022 [3 favorites]

Response by poster: @dusty potato This one is where 7th Avenue meets East 20th Street in Oakland. A nearby house is at 2002 7th Avenue.
posted by sugarbx19 at 4:55 PM on April 24, 2022

Best answer: IAMATrafficEngineer, but could you be thinking of the slightly more generic (than diagonal traffic diverter) term "turn island" or "forced turn island?"
posted by JackBurden at 4:55 PM on April 24, 2022 [3 favorites]

Traffic Management, at the DOT: Diverters (Diagonal, Star, Forced Turn and Truncated)
posted by Iris Gambol at 5:11 PM on April 24, 2022 [8 favorites]

@dusty potato This one is where 7th Avenue meets East 20th Street in Oakland. A nearby house is at 2002 7th Avenue.

Wow, this is interesting! It's not actually a vehicular intersection at all, right? Basically a blocked-off node of the grid system?
posted by dusty potato at 5:20 PM on April 24, 2022

Best answer: It is a vehicular intersection based on the cars in Google street view here . I found the original description succinct and clear. Vehicular traffic from 7th ave must turn onto 20th street one way or the other, no matter how they approach.

Idk what it's called but I tentatively like what I think the idea behind it is, not sure if it's effective as deployed or not. A good name could help us find research on the topic.

So far "forced-turn diverter" seems descriptive and useful.
posted by SaltySalticid at 5:56 PM on April 24, 2022

Oh hi, neighbor. Would you believe one of these diverters (5 blocks from the one in your pictures) got its own MetaFilter post in 2014?

I once had the amusement of observing a car chase interrupted by one of these things. I watched the first driver, clearly unfamiliar with the neighborhood, turn off the main thru street right toward the corner with the forced turn, cops in pursuit. Thirty seconds later, both cars came around again...
posted by aws17576 at 8:08 PM on April 24, 2022 [6 favorites]

99 times out of 100 these were originally normal intersections, but for whatever reason (neighborhood complaints, usually) they force these turns to dissuade people using side streets as a bypass of an arterial.

I hate em. Makes it hard for emergency services to navigate.

But, I never knew they had a technical name. I always just thought of them as closed roads.
posted by hwyengr at 8:12 PM on April 24, 2022

It is literally a diagonal diverter and that term is used by many DOTs across the country. It's called that because the barrier to cars cuts diagonally across the intersection. The road turns, cars remain in their lanes, no one turns out of their travel lane because the whole road goes around the corner.. In many case cyclists can continue through the barrier.

A forced-turn diverter or forced-turn island blocks certain approaches to an intersection, by forcing some lanes to turn, i.e. traffic from the west may be able to move straight through an intersection, but traffic from the east must turn onto the crossing street.
posted by oneirodynia at 10:22 PM on April 24, 2022 [3 favorites]

Oh dang, the link I posted above clearly supports oneirodynia, it's a diagonal diverter. I failed to read it clearly!
posted by SaltySalticid at 7:53 AM on April 25, 2022