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New research says ‘left turn calming’ makes intersections safer

Posted by on April 15th, 2020 at 1:32 pm

(Graphic: IIHS)

Good news for the Portland Bureau of Transportation: One of their newest tools to improve crossing safety at intersections just got a stamp of approval from new research from the nonprofit Insurance Institute for Highway Safety (IIHS).

Centerline hardening in action on North Williams and Killingsworth.
(Photo: J. Maus/BikePortland)

Last summer PBOT rolled out a new type of speed bump they call ‘left turn calming’. These rubberized bumps are placed in intersections where car users tend to turn left too quickly and/or cut the corner. The idea is that the bumps force people to make sharper turns, drive at slower speeds, and have better visibility of people in the crosswalk.

According to new research from Washington D.C., this “centerline hardening” treatment is associated with a 70.5% decrease in conflicts between drivers and crosswalk users. A paper published this month by IIHS-funded researchers Wen Hu and Jessica Cicchino, also found that the bumps lowered mean left-turn speeds by nearly 10% and reduced the odds of people going over 15 mph while turning left by 67%. Hu and Cicchino studied 10 intersections in D.C.

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Left turn collisions are the bane of traffic safety advocates. In 2018 they accounted for almost one third of all intersection collisions nationwide that involved a person on foot. According to State of Oregon data, 20% of crashes involving walkers (between 2006 and 2015) were the result of left-turning drivers failing to yield to people in crosswalks at signalized intersections.

Last year PBOT installed left turn calming bumps at over two dozen intersections citywide. Learn more on their website.

— Jonathan Maus: (503) 706-8804, @jonathan_maus on Twitter and jonathan@bikeportland.org
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grrlpup
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grrlpup

Love these. The similar right-turn calming from SW 4th onto eastbound Market has made a big difference to me as a pedestrian.

Steve Hash
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Steve Hash

I love them too, but they seem to be encouraging drivers into the bike lane at Willamette and Portsmouth (though I guess, in theory, the bike lane should be empty if the car turning has a green light).

Hello, Kitty
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Hello, Kitty

I see plenty of drivers blissfully drive over them, but every bit helps. I think they look pretty sharp as well.

Kittens
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Kittens

I think this is one intervention from PBOT which is making a big difference. Of course some people run over it with no concern, most do not. I think a lot of people are just getting used to them and adapting.

J_R
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J_R

Probably one-third of the plastic wands used to create a “protected” bike lane on SE 45th Avenue are missing. At least the bumps will stay a bit longer. I am skeptical that the bumps will have a long-lasting impact on driver behavior.

Suburban
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Suburban

How quaint that the first image shows an automobile turning left into the near lane. That must be some hold-over technique shown in a drivers manual somewhere.
Interesting note: 31% of traffic tickets written in Portland, Gresham and Beaverton (no data for Tigard or OC) are for failure to turn into the near lane.

Johnny Bye Carter
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Johnny Bye Carter

They added this northbound on SE 99th turning left onto SE Stark. It makes it impossible to make a left there without going into the other lane. There’s no turn radius, at all. I don’t think they thought this through for 1-way streets. You end up having to do a button-hook turn, which makes me uncomfortable.

Middle of the Road Guy
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Middle of the Road Guy

I think these are good cheap methods. A similar installation slows down the right hand turn from Interstate to Mississippi – a turn people used to take a high speed.

FDUP
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FDUP

If you hit one of these on a bicycle, which isn’t hard to do, you’re going to hurt yourself.

todd.boulanger
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todd.boulanger

It is amazing what a bit of intersection geometry tweaking can do when you work with physics AND are motivated to prioritize traffic safety solutions over other mid [last] century objectives like vehicular capacity or “maintenance”.

These type of mini mountable extensions are called “hedgehogs” in the UK.
What shall we call them in the NW? …Marmot? Otter? Beaver?

Jay Sayles
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Jay Sayles

These rubber bumpers have created problems at intersections that didn’t previously have issues. The ones located at SE 30th and Hawthorne have increased congestion at that intersection and force pedestrian and bike traffic to interact more directly with vehicle traffic. By attempting to direct vehicle traffic into a narrower area that also directly competes with the oncoming traffic these make the streets more dangerous. I’ve seen more close calls and all road users confused by the changes.

The bumpers also force cars attempting to make left turns in opposing directions into the same space where they previously could avoid each other and other road users. Also since these reduce the number of cars that can make it through the intersection each light cycle and creates backup it directs more cars into the smaller residential streets and adjacent bicycle greenways on SE Salmon and SE 29th Ave. A poor design decision that is causing more problems than solutions.

JR
Guest
JR

I have noticed these out on the streets. In some locations, it doesn’t seem possible to make a left turn simultaneously with the opposite direction left turning vehicle because you have to drive further into the intersection. It certainly does cause one to slow down more. It’s also a bit of a distraction if you try to avoid running over them, looking for cars turning in the other direction and pedestrians.

AndyK
Subscriber

More, please! These devices have very little downside.

Chip
Guest
Chip

Saw a nasty T-bone accident the other day on 92nd and Foster, likely this little bump had a part to play. Sedan from 92 turning onto Foster got hit by another driver who swerved around a bike, while forcing the yellow. 92.d Ave driver was too far into the intersection in order to go around this little bump, and took longer to make the tight turn as a result, saw the swerving car in the opposite lane too late, and bam. both cars with popped airbags and police + tow trucks. I get why they placed them here, but it restricts movement and turning circle. And these were a car and a small SUV, not some monster truck towing a trailer… Roundabouts are way safer than restricting lanes, see Bend!