
Could These Intersections Make Us Safer? (2013) - hexane360
http://www.citylab.com/cityfixer/2013/01/could-these-crazy-intersections-make-us-safer/4467/
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ethagknight
As a former transportation engineer, I always notice and despise whenever we
get overly creative. Could that intersection make us safer? Yes, for all the
experienced locals, but absolutely not when you factor in a handful of old,
drunk, texting or otherwise unfamiliar drivers, for which it looks like a
head-on-collision demolition derby.

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a2tech
Agreed. I despise locals only solution. The city I live in has passed a new
law in the last 2 years that traffic needs to stop for any pedestrian
approaching a crosswalk. This has led to a ton of weirdness such as: how do
you know if a pedestrian is intending on crossing? do you stop on a fast one
way street when someone might be contemplating crossing? People that aren't
from the city of course don't know anything about this local law so they drive
like normal..which means they don't expect people to come to a complete stop
in the middle of a bustling road for no apparent reason. And as a pedestrian
its worse-you can't trust the cars to stop (because not everyone knows the
law) so you just linger at the edge of the road until everyone stops
(hopefully). Its ridiculous.

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varjag
Amen, regulation like that should be introduced nationwide. Pedestrian
priority isn't a new concept and works just fine in many countries, but can't
imagine it pocketed to a city and work.

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dhimes
Agree. We are just having an over-reaction to people stepping in front of cars
and getting hit. They seem to think their pedestrian rights will stop a car
that is too close for a driver to be able to react. I'm watching people with
earbuds walk into an intersection _without even looking._ We teach defensive
driving; we need to teach defensive walking, it seems.

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maxsilver
If your intersection is busy enough to justify some of these rather large and
expensive intersection designs (like #5 and #13 from the article) -- then you
might as well spend the cash to make it into a real freeway interchange and
have zero intersections or stoplights at all.

That will handle even more traffic, be even safer (by their geometric conflict
metric), have no stoplights for drivers to deal with, and no one has to learn
anything new to navigate it safely.

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crashdown
The Magic Roundabout
[https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)](https://en.wikipedia.org/wiki/Magic_Roundabout_\(Swindon\))

That is all.

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giarc
>has an excellent safety record, since traffic moves too slowly to do serious
damage in the event of a collision.

I guess that's another way to prevent accidents. Confuse and slow people down
so much that if accidents do happen, they happen at 2km/h.

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kirushik
Also known as traffic calming:
[https://en.wikipedia.org/wiki/Traffic_calming](https://en.wikipedia.org/wiki/Traffic_calming)

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RankingMember
My first thought looking at the long ramp for right turns is that people are
going to miss them and then make their right turns where they normally would
(the "dangerous" way).

New Jersey has a lot of this and it results in people reacting by whipping
U-turns either in the middle of the road or needing to whip around in random
parking lots and then try to cross 2 lanes of traffic to go the other way to
get back to the turn they missed.

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phkahler
I've spent some time thinking about roadways, and I've decided the problem
starts at a much higher level. When I'm traveling down the road it should be
easy to get to the place I want to get, or onto another road that I need to
get on. It seems the thing closest to me though is the LAST thing I want - a
lane for going the opposite direction. If I'm going west, I don't want to go
east, yet a few feet away is a lane going east. If I want to turn south, I'm
going to have to cross that lane going east. This is why we have intersections
and accidents.

If you look at the EPA fuel economy standards, they run cars on several
different cycles representing different driving conditions. In particular
there is a highway cycle and an urban cycle. When I worked in EVs I was
stunned to find that the average speed on the urban cycle is a hair short of
20mph. You'd think with typical speed limits of 45mph it would be much higher,
but with all the stopping and going you waste a lot of time and fuel. The main
reason hybrid cars get better mileage is the recovery of kinetic energy when
stopping. It seems we're demanding cars make up for deficiencies in roadway
design, but that only helps with fuel, no peoples time.

So If we made a lot of one-way roads with the right nested structure (I'm
playing with long ovals) we could eliminate a lot of intersections where lanes
cross. Your travel distance might be 10 percent longer, but your time on the
road could be reduced significantly. You'd also have to learn a slightly
different route for going somewhere and coming home. Another aspect of
reducing travel time is that with cars on the road for half the time, you'll
have half as many cars on the road at any given time and that means you can
put down half the pavement. Getting it right would be a huge win all around.

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bryanlarsen
"huge win all around"

Sure, if you're designing a cars-only freeway. Once you add pedestrians, one
way streets dramatically increase the fatality rate. Cars are going faster
(dramatically increasing the risk of fatality), and are generally only looking
in one direction, so don't see pedestrians coming from the other direction.

~~~
phkahler
>> Once you add pedestrians, one way streets dramatically increase the
fatality rate.

The key is not to put the pedestrian paths next to the roads. That's similar
to putting the opposing traffic right next to the road.

Imagine a suburban neighborhood where the sidewalks run through the back yards
instead of out front by the road. You have branching walkways that are the
inverse of the branching roadways. Now start to design high density cities
along similar lines, where pedestrian areas connect high-density buildings in
a sort of fractal pattern with roadways around the outside (one way of course)
and branching in between the fractal stuff. You can add pedestrian bridges in
key places if desired.

I don't think a large 2-d area with high fractal dimension makes the most
sense, it should be more like a long strip with bulbs off the sides. These are
then surrounded by an oval roadway with intruding branches. You lay multiple
ovals next to each other and have a larger oval connecting them all at the
ends - a perpendicular oval. Something like that.

If you think about how blood circulates in the body, it's a hierarchy of
different sized arteries and veins. You can get from any capillary to any
other by just going around the system one time. Now imagine you put a loop at
each level of the hierarchy so you don't need to go all the way to the top
level - long trip. If your try to lay that out flat there will be some
intersections, and you may still have things close together that are
topologically farther apart - it's when you start making those short
connections that you create intersections and congestion which starts to
destroy the efficiency.

I'd also prefer a fractal-like city with green space mixed in, so perhaps
those ovals should not be side-by-side, but sprawling. How about _all_
buildings are high density (so public transit makes sense) but the overall
density is more like the burbs? Clusters of towers in the woods or open areas.

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dragontamer
There are roughly two diverging diamonds within ~30 miles that I'm aware of.

Its utterly insane to break the "Right-side driving" rule. I know people who
have literally driven on the wrong side of the road through a diverging
diamond.

Perhaps it is "theoretically" safer once everyone knows how the hell it works
(I mean, yeah, now that I know I need to drive on the LEFT side of the road
through a diverging diamond... it makes sense). But jeez, it takes some
getting used to.

\----------

I worry about tourists and newbies who will also drive on the "right" side,
and completely break the diverging diamond. Fortunately, the "better"
diverging diamond that I'm aware of is only a 3-way intersection, and there
are very tall walls that "blind" you to the fact that you're driving on the
left side. It works very well.

The 4-way diverging diamond: where you drive on the wrong side of the road for
an extended period is simply insane... at least the first time you go through
it.

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JoeAltmaier
That mess turned a single intersection into...let me count...16 intersections.
I'm baffled. How is that safer?

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phil_s_stein
It minimizes left-hand turns across oncoming traffic that has a green light.
i.e. it minimizes human judgement. If everyone stops at red lights (and people
are very good at that), then there are fewer or no places where traffic
crosses paths at the same time.

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athenot
The article mentions roundabouts being the holy grail then faults them for not
being able to handle capacity. But in Europe, it's quite common to have high
throughput roundabouts, with multiple lanes.

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nothrabannosir
But then you get many more collision points back. The definition of roundabout
in this article is in terms of collision points, i.e. safety.

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legulere
Another issue is that they take up a lot of space which might not be there.

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ytjohn
Probably would take up a lot less space than the article's proposed mega
intersection.

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rubidium
I despise the Michigan Left. There's one by a critical gas station (i.e. "I'm
often running out of gas when I'm near it"). But I can only get to it if I'm
going the correct direction.

Otherwise I have to wait for the light, go through intersection, pull a
U-turn, wait for the light again, go through the light, pull into gas station,
pull out of gas station, pull a U-turn, wait at the light, and I'm finally on
my way again.

While it may be safer, the Michigan left has got to kill any business located
near the intersection.

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maxsilver
> Michigan left has got to kill any business located near the intersection.

Many businesses actually prefer those locations, since "Michigan left"
intersections can handle large amounts of traffic safely. (In Michigan, nearly
all major retail centers are on or near these roads).

> There's one by a critical gas station (i.e. "I'm often running out of gas
> when I'm near it").

You could just buy gas on your return trip. If your often on the "wrong side"
of the street for the station, your return trips would presumably put you on
the "right side" equally as often.

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dragontamer
Or more likely, if an intersection requires a Michigan Left, there's probably
enough traffic to warrant two gas stations.

Of course, those two gas stations will have different prices, pissing off
everybody. I'm not speaking from experience or anything...

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NoGravitas
The "Michigan Left" was used a lot in New Orleans when I lived there. I didn't
know there was a name for this pattern.

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mholmes680
I have some random thoughts:

a) where the heck is everyone going anyway? Can people simplify their lives by
efficiently picking routes - and getting them all done in a chain?

b) If autonomous cars are the future, they eventually get some say in how to
efficiently structure roads, right? So, will some AI one day figure out that
the greater "hive" will all benefit if every car only makes right-hand turns?
And do left hand turns just become illegal?

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camiller
With good AI anything is possible:
[https://www.youtube.com/watch?v=4pbAI40dK0A](https://www.youtube.com/watch?v=4pbAI40dK0A)
see the simulation at 0:55.

~~~
mholmes680
oh wow, nice reference. but, then you have a car thief use case, and it screws
the whole thing up! :)

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Shivetya
In Georgia our fascination is now with Diverging Diamond Interchanges, one is
active and another is being placed at Windy Hill and I75. Should be
interesting at that location as currently traffic in the area is just murder.
Some smaller roads have gotten roundabouts where traffic lights didn't make
sense and four way stops were impeding the flow

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dbg31415
They built one of these jughandle intersections near me. Maybe when we have
self-driving cars it'll make sense. It takes much longer to get through it, I
feel, and it backs up often. Not a fan.

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ChoHag
I've driven through most of these in various parts of England and many
variations on them. I think it's safe to say there's usage data to be
consumed.

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stuaxo
I've seen this conflict junction in paris before

[https://vimeo.com/57972903](https://vimeo.com/57972903)

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ocschwar
That is a lot of acreage devoted to that intersection.

Something you should know about land: they ain't making more of it.

