[Off-camera:] It's gluten-free!
If there's any highway design feature that's in vogue right now—
that traffic planners want to put in—
This is it!
Wisconsin alone, I heard at a conference I attended last week,
installed hundreds of roundabouts just in the last 15 years.
And if that's Wisconsin, how many more of these things have been built,
are being built, and will be built in the United States in the years to come?
Now when you hear that fact, it probably evokes one of two emotions:
Either you think: "Oh, roundabouts! Those are great. They're so European!"
Or it makes you think, "More roundabouts? Yuck! They're so... European!"
So today, once and for all, I'm going to answer the question:
Are roundabouts great or terrible?
[Video game:] "Three... two... one..."
[Video game:] "Fight!"
The Washington State Department of Transportation compared regular
intersections with roundabouts to see if roundabouts were safer.
And they found roundabouts have a one-third reduction in traffic accidents—
cars hitting pedestrians, cars hitting cars,
cars hitting telephone poles— it drops over 30%.
But here's the real kicker: when it comes to fatal accidents,
roundabouts reduce them by over 90 percent.
Part of what makes the roundabout so safe too is that traffic all has to slow down—
everybody's going through this at about 20 miles an hour.
A roundabouts is the great equalizer,
because what causes serious accidents isn't necessarily speed—
you can have two cars sights wipe each other on the freeway and everybody walks away fine—
The nice thing with the roundabout is we all end
up going about the same speed. The roundabout requires it.
You think about what causes a fatal accident:
T-bone crashes? Hard to do that when you have to slow down and go around a big planter box.
And the planter box is in the way.
But in order to get cars to slow down, you have to go around a fairly tight circle.
And that's not real compatible with big rig trucks.
Just about every well-designed roundabout you'll
encounter has the sidewalk sort of apron in front of the planter box.
It allows the back wheels of a semi that the trailer to kind of
"off-track" as they're coming around navigating this thing.
And the big semi wheels have really no problem getting over this kind of beefy curb here. You
and I, in our regular cars, we try to drive over that we definitely feel like, "oh yeah,
I'm in the wrong place. I shouldn't be up here."
Being a big circle, you don't typically see roundabouts in downtown areas because they
take a lot of space. But the other reason too is pedestrians have a long walk to go around them—
and that's not really useful in areas with high amounts of pedestrian traffic. To demonstrate:
Okay, I'm walking down the street from the roundabout to the regular intersection.
One, two, three...
Around 60 steps to get across a regular intersection.
...114, 115.
One-hundred and fifteen steps. That's almost twice as far to cross the street [using a roundabout].
One of the problems is that encourages people not to cross properly.
A roundabout is cheaper than a traffic signal and what I mean by that it's not really that
it's cheaper to build it cost about the same as a traffic signal to install,
but when you put a traffic signal in you have controller equipment
and you have to time the lights and you have to maintain it—
And you have to pay for electricity, which runs between $5,000 to $10,000 dollars per month,
depending on how expensive electricity is in your city.
A roundabout, you build it and you just kind of let the thing run.
So what do you do when your street gets busy enough that the little
one-lane roundabout doesn't cut it anymore?
The line just to get into the roundabout or backing down the block.
Well, you can put in a two-lane roundabout or three-lane roundabout. As an added bonus,
these provide ample space for semi trucks to go through.
But, there's a catch—
Multiple lane roundabouts are not quite as good for pedestrians.
As you saw there, the traffic didn't stop for me. I had to wait.
And so, I think some of the advantages are lost. If you're driving through here
by yourself and you have two or three lanes, I'll just kind of hug one side and then as we
come around the circle a hug the other side and then hug back the other side—
I kind of straighten out the road. And as drivers do that,
you lose that safety advantage of everybody slowing down for the roundabout.
The problem with these is— there starts to be a learning curve. It gets a little confusing
knowing which lane you're supposed to be in, which lanes gonna go left and back around the circle.
[Wisconsin TV spot: "...take it slow. Pick the correct lane and take it slow."
So, when a community is getting ready to put in its first roundabout—
it's best to probably put in a single-lane one rather than putting in a complicated
one with multiple lanes. That way you cut the learning curve down just a little bit.
I'm standing on a construction site in the South Valley of Salt
Lake City where there used to be a big roundabout—
I called it an "oval-about." Not sure it's supposed to be called that.
And it's being removed and replaced with a set of stoplights.
Why are they pulling it out?
[Emperor Palpatine:] "UNLIMITED POWER!"
To really get into one of the advantages / disadvantages of roundabouts,
we have to get into a little bit of traffic flow engineering.
In traffic flow, there are platoons and there is random arrival.
Random arrival: cars just kind of show up randomly.
Platoons: when cars get in little bunches caused by traffic signals.
We all arrive randomly, but as we're sitting there waiting and waiting, we build into a
little bunch. And then when we get a green we can move together as a bunch down the street.
But in order to make platoons work, roads have to be really fast they have to handle
that big bunch coming down the pipe all at once.
So why do traffic engineers put cars into platoon bunches in the first place? Well,
this is this neat little thing called "signal progression."
If you can get this bunch to all take off at the same time from one green light,
you can time it just right so that bunch gets the next green light, and the next green light,
and the next green light— and the theory is that a car
going the speed limit down the street may make five green lights in a row.
That's why roundabouts don't work on every type of road. Some roads,
the one set up for bunches of platoons to get green after green after green
after green in a progression— Well, a roundabout messes that all up.
Now, your beautiful little platoon is now random again. It's scattered.
You could always go to the other extreme and do what Carmel,
Indiana did. Eliminate ALL the traffic lights and replace them
all with roundabouts. That way platoon travel was just eliminated from the city entirely.
I guess it's time we finally decide once and for all our roundabouts terrible or great?
And the answer is, they're great— if you put them where they're supposed to go.
A little bit of bait and switch. The answer is
roundabouts are great when they're used appropriately.
According to this very "scientist-ish" graph I made, roundabouts aren't great
where there's lots of pedestrians downtown you're a train station but as you start
to get into the neighborhoods that we can work pretty well.
Roads that carrying lots of cars:
arteries and expressways, really do need to rely on platoons to keep the traffic moving
So, that's where I would personally start dialing back from the roundabouts.
And definitely don't put any roundabouts on the freeway.
Did I get this right? I forget something? I often do. Post it the comments below.
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