Could These Intersections Make Us Safer? (2013) | Hacker News Reader

Could These Intersections Make Us Safer? (2013)

citylab.com

29 pointshexane36046 comments

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.

I just made a separate comment about this but wanted to chime in and agree; locals will learn the new traffic patterns but everyone else will be confused. This confusion can result in panic and, ultimately, accidents. I don't know if you've driven in New Jersey (South Jersey's what I'm familiar with), but it's a good example of some of these types of irregular patterns (e.g. long ramps for turn-offs).

They seem to design these for a perfect world where everyone is paying 100% attention to signage (and signage is never obscured/missing/confusing itself).

One source of panic: turning left now you can be faced with 4 or 6 options of where to go, instead of two. If you just get it wrong, you're going the wrong way on a one-way lane.

Also, give it a few years for the guiding lines to get nice and faded. Maybe some rainy weather to erase them from vision completely.

This intersection would definitely get safer because I would avoid it completely.

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.

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.

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.

Completely agree. But it can take a lot of time before locals get used to new driving as well. Really, anything besides standard intersections will cause more headache than good because humans don't like change. How safe is the safest intersection - The one without humans. Humans need simple fast intersections that they can take in only enough information that is processed without complicated thought. At this point in infrastructure and human driving, we should not introduce new anything.

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.

The Magic Roundabout https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)

That is all.

>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.

Also known as traffic calming: https://en.wikipedia.org/wiki/Traffic_calming

What about it?

(As a former Swindon resident who used to cycle across it with an E-flat tenor horn strapped to the rack, I don't really have a problem with it)

I just wanted to show it to people who have not seen it before. It is a marvellous invention :D

No, single roundabouts are annoying enough. Give me a stop light or a 4-way stop.

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.

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.

"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.

>> 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.

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.

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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.

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

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.

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.

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.

A turbo roundabout can have physical separators. And there are other variations; for example in my city there's a large one with two isolated circles (you chose the circle before entering the roundabout, depending on where you want to go).

But all those roundabout collision points are very minor threats compared to a left hand turned slamming into a red-light-runner. I'll take 50 chances of bumping side panels with someone on a roundabout compared to 1 chance of getting t-boned at a left turn.

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

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

French traffic engineers love roundabouts. Actually, they are indeed safer that plain intersections. What I despise, though, is that too often building a roundabout coincides with giving up any effort to try and manage the traffic at intersection. Having heavy traffic in one direction on a national route yielding to cars leaving the parking of a mall, while the other direction flows undisturbed, is not nice at all. Especially if you are on the wrong side of the national route :-)

Roundabouts in Europe are being pulled out. They have a narrow band of efficiency, between TooMuchTrafficForAStopSign, and ConstantTrafficPreventingOneDirectionFromEntering. So they get built one year, and a few years later pulled out.

In my growing town they're being built like sausages. I have to negotiate several a day. Most days the guy in front of me comes to a full stop, even when nobody is on the circle at all. If I'm not alert its dangerous - somebody stopping dead in the road for no reason.

In a couple of years I look forward to them being removed.

What are they being replaced with? Even a roundabout with traffic lights regulating traffic entering it seem safer and more efficient than a pure traffic light intersection.

Traffic lights. Left-turn lanes.

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.

But you have the same issue even without the Michigan Left, but even worse because there is no way to get to the gas station (without finding a parking lot to turn into and turn around).

Consider an intersection that is busy enough to have a raised median. The gas station is on the left hand side, before the intersection, on the corner. You can't get to it before crossing the light, due to the raised median. You also can't turn left at the intersection and cross over, because of the raised median on that road. So you have to drive down the road a piece, find a safe way to get going in the opposite direction (like pulling into and out of a parking lot), then do the same dance after the gas station visit.

> 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.

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...

Or don't wait until you are critically low on fuel to stop.

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.

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?

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

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

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

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.

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.

I've seen this conflict junction in paris before

https://vimeo.com/57972903

That is a lot of acreage devoted to that intersection.

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

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