Traffic flow measured on 30 different 4-way junctions
December 6, 2017 12:42 PM   Subscribe

A soothing six minutes of traffic flow simulations using traffic mods for the game Cities: Skyline. (slyt)
posted by bondcliff (51 comments total) 42 users marked this as a favorite
 
An extremely excellent previously.

I found this old post over the summer, fell in love, and bought a whole new computer just so I could have something robust enough to play this game.
posted by phunniemee at 12:57 PM on December 6 [2 favorites]


DIVERGING WINDMILL WHAT R U DOING?
posted by GuyZero at 1:00 PM on December 6 [2 favorites]


The turbo roundabout is terrifying.
posted by jeather at 1:04 PM on December 6 [6 favorites]


Why did I say "Woah. They did it!" when the traffic flow broke the 500 mark? How did you get me this invested in this video?
posted by robotmachine at 1:08 PM on December 6 [5 favorites]


Original reddit thread

I haven't touched the game in a while but the sub is quite interesting with all the cool stuff people create.
posted by MillMan at 1:09 PM on December 6 [1 favorite]


I think that roundabouts would have had a better showing if the drivers weren't terrible. Learn to merge, people!
posted by CaseyB at 1:11 PM on December 6 [6 favorites]


Car flow simulators! /beanplate

Actual traffic flow (e.g. people per hour) depends on how many take transit or bike, not twiddling with layouts of sprawling car intersections.
posted by anthill at 1:18 PM on December 6 [7 favorites]


I think that's a French roundabout, where, once you are in the roundabout, you must stop for any traffic coming in from the outside ramps. In other countries, like the US and UK, you do not need to give priority to traffic from the right and you may simply keep going in the roundabout to your heart's content, until you are ready to leave. What I'm saying, basically, is that if you rent a car in France, just buy the full insurance package and let the driving gods handle the rest.
posted by a lungful of dragon at 1:18 PM on December 6 [10 favorites]


Very cool! It's funny that accurate traffic simulation is usually the most complex of city sim games.
posted by Foci for Analysis at 1:21 PM on December 6 [1 favorite]


"no no no no no no no no"
-- Me, the first time I drove through one of those diamond interchanges to the left side of the road
posted by middleclasstool at 1:26 PM on December 6 [3 favorites]




Being the public transit fanboy I am, I look at this and can only see the increasingly crazy amount of land needed vs. incremental gains in traffic throughput.

Cities: Skylines is an awesome game though.
posted by fnerg at 2:04 PM on December 6 [14 favorites]


What about the Pittsburgh solution, which is the combination of stop signs at the end of most of the Parkway onramps, combined with the placement of a given onramp entrance just prior to the same exit's offramp, such that you have to accelerate from a dead stop to freeway speed while dodging people trying desperately to cut you off to make their exit? Then, just for kicks, do all of that 100 feet before the entrance to a tunnel.
posted by namewithoutwords at 2:09 PM on December 6 [5 favorites]


One of the cool things about Cities: Skylines is that if you build a solid path infrastructure your little cims will nearly always default to walking or biking.

It's just more fun watching car flow simulations.
posted by phunniemee at 2:10 PM on December 6 [4 favorites]


Can you imagine being from out of town and hitting that turbo roundabout? Shitshow.
posted by stinkfoot at 2:41 PM on December 6 [1 favorite]


Wow the last few are really beautiful... and they definitely sandbagged the final traffic flow number for an extra second or two.
posted by stinkfoot at 2:45 PM on December 6


I love the threads on reddit that are people (in magical lands where you are given nice long entrance ramps and plenty of time to merge) asserting that you must get up to highway speeds when merging, and the inevitable posting of the onramp stop sign right before the Squirrel Hill Tunnel. I lived right by there for a number of years so I have a particular fondness for it.

A large number of the roundabout interchanges did seem like they required a little too much knowing what you're doing. The turbo roundabout definitely would have people slowing down and having no idea what they're doing and trying to make u-turns in impossible places.
posted by that girl at 2:45 PM on December 6 [3 favorites]


Oh god that game.

I bought it two winters ago, and sat down on the couch to play it one evening around six. The thing about the game is there's always something to do -- your city needs more power, it needs more water, there's a vacant building that needs to be demolished, your people are unhappy because it takes them too long to get to the hospital. A continual stream of tiny things to fix as you construct your city. It's hypnotically meditative like driving cross country or playing Sudoku.

A short while later, I was yawning a bit as I oversaw my glorious city of 250,000, built meticulously out of progressively denser rings of freeways and trains and apartments and factories. Little boats came in and out of the seaport, airplanes took off and landed at the three airports. Good health, plenty of money in the bank, power and water were all OK. I stood up to go to the bathroom and looked outside -- the sun was rising. It was 7 am.

The game is still on my computer but I haven't touched it since.
posted by miyabo at 2:47 PM on December 6 [13 favorites]


They put in a diverging diamond here in town this spring, and I'm not sure it's that much of an improvement, but I will say that during the first week it opened, every time I drove through it (about 5-6 times) I encountered one car going the wrong way, having ignored the many signs and the tough corner to get back on the "correct" side of the road.

And, having driven through a lot of the upper midwest, I have to say: the more complicated those interchanges are, the further ahead you need to make absolutely sure you're in the correct lane, otherwise it's a looooong way before you can turn around, and I'm pretty sure those traffic estimates don't include the number of people who have to go through the exchange more than once because they couldn't get into the correct lane the first time around.

also, the simulation video showed a lot of vehicles passing through each other, which I'm pretty sure I can't actually do, although I wish I could at many intersections
posted by AzraelBrown at 2:57 PM on December 6 [3 favorites]


UDOT is a big fan of testing continuous flow, diverging diamonds, and Michigan left intersections lately. I hope nobody shows them this video or I'll be subjected to a turboabout on my way to the grocery store.
posted by msbutah at 3:19 PM on December 6


Finally, something in my wheelhouse.
posted by drezdn at 3:59 PM on December 6


I need to buy Cities Skylines.

I also found the traffic video linked vastly more entertaining than I feel I should have.
posted by sotonohito at 4:32 PM on December 6


I believe the Gothic Cross is actually more efficient than anything he's shown in that video - here's an example of one that I built - excuse the mistake in the onramp in the bottom left.

Even the full stack interchange he shows at the end is only semi-directional, while the Gothic Cross is fully directional. There's "kind of" one example somewhere in Michigan which I found while scouring Google maps. Interesting, the English wikipedia doesn't have an entry for the Gothic Cross, while the German version of wikipedia does, which is how I found it.
posted by xdvesper at 4:38 PM on December 6 [3 favorites]


***reinstalls Cities: Skylines***
posted by Fizz at 4:40 PM on December 6 [2 favorites]


Also the Gothic Cross wouldn't look like that in real life (9 lanes converging into 3 at the same point) but that's just a limitation of the base game... I suppose we could do it with self driving cars!
posted by xdvesper at 4:41 PM on December 6


That video. I am in a trance.
posted by Songdog at 4:52 PM on December 6


I need to buy Cities Skylines.

Bad/Good news: it's on sale on Steam.
posted by GuyZero at 4:54 PM on December 6 [4 favorites]


This video is really making me want to play this game now, I haven't played a city-building toy since... the Amiga version of Sim City, most likely.

It's on sale on Steam right now, too. Seven bucks plus maybe some DLC and how can I resist.
posted by egypturnash at 4:58 PM on December 6


That was really interesting, especially learning some interchange taxonomy.
posted by lucidium at 5:15 PM on December 6


I'm kind of curious, a lot of these are designed with a human driver in mind. There is a lot of psychology and theory and practice surrounding human drivers reacting with their messy monkey head-meats when going from one road to the other. You are assuming a lot of bad actors, whether deliberate or unknowing. That's modeled into the game.

What would these interchanges look like, if they had a self-driving system with pinpoint precision, open communications with other vehicles, and a from-the-factory government mandated traffic etiquette baked in?

Would we need these fancy interchange designs at all, or would the designs be fancier and in incomprehensibly stranger ways?
posted by Slap*Happy at 6:09 PM on December 6


The DLC will likely go on sale within the month so don't grab any yet -- but the base game price has been the same at every sale for awhile now, so it's a good bet.
posted by curious nu at 6:20 PM on December 6


Slap*Happy There's some speculation that in a fully automated driving future you wouldn't need stop lights and so forth because traffic would be spaced to let cars just zip through the intersections between other cars, vastly simplifying interchanges.
posted by sotonohito at 6:54 PM on December 6


This is a lovely video to watch and be entranced by. It's also a good reminder that city simulators still tend to be too focused on car travel and road traffic for my tastes, though Cities: Skylines is still better than most. And you'd hope so, coming from the same people who did the Cities in Motion transit planning simulator series.

As mentioned above, Cities: Skylines does seem to encourage its citizens to walk around whenever possible (and SimCity wasn't too shabby at this either), but city sims have traditionally been poor at allowing people to design actual pedestrian flows. Buildings necessarily tend to be cookie-cutter (i.e. no carefully designed, site-specific layouts for metro stations or skyscraper plazas), and pedestrian-level route design is usually too small to be adequately accounted for in city sims for the most part, especially the sort of complex urban labyrinths you'd find in large cities. That's not intended to be a knock against Colossal Order or (RIP) Maxis, more a desire for a higher level of city sim complexity that we'll probably never reach because by that point you're almost literally simulating a city, which means a) you'd need so much computing power you could probably make a fortune in bitcoins instead, and b) you could probably be an actual city planner.
posted by chrominance at 7:04 PM on December 6 [1 favorite]


Yeah, C:S takes pedestrians more seriously than other modern-era citybuilders in the sense that it considers them at all, whereas the SimCity games have generally been content to tack sidewalks onto roadways and call it done. However, all the pedestrian walkways in C:S have essentially infinite pedestrian capacity and, as far as I can tell, the same walking speeds (i.e. desirability for pedestrian route-finding algorithms). This stands in contrast to the roads, which all have detailed modeling of capacity and travel speed (both marked top speed and the real speed when accounting for congestion).

The base game doesn't include any congestion charging or service/delivery-only roads, though. (After Dark adds a policy which can be used to define districts where only residents and businesses can use the roads, though.) Or mixed zoning. Or even toll roads, now that I think about it. So while people have built some pretty impressive transit-oriented cities (including some with no external highway connections!), there's still a lot of concepts in modern urbanology that aren't represented.

For those wondering which DLCs are "mandatory", I'd put After Dark at the top of that list, just because it adds dedicated bike lanes and policies related to them, in addition to dedicated bus lanes. Mass Transit adds some new transit hubs and road types, so that's probable the second most mandatory. I don't actually have it, though. The other three are more oriented around specific concepts, so you can take or leave them based on whether those concepts appeal to you. (Though it's mildly annoying that street-level trams are bundled in with Snowfall, because all of that DLC's other features only apply to the new snow maps.)
posted by tobascodagama at 7:26 PM on December 6


What about the Pittsburgh solution, which is the combination of stop signs at the end of most of the Parkway onramps, combined with the placement of a given onramp entrance just prior to the same exit's offramp, such that you have to accelerate from a dead stop to freeway speed while dodging people trying desperately to cut you off to make their exit? Then, just for kicks, do all of that 100 feet before the entrance to a tunnel.

I drive through that almost every day and had almost forgotten how insane a design it is.
posted by octothorpe at 8:09 PM on December 6


""no no no no no no no no"
-- Me, the first time I drove through one of those diamond interchanges to the left side of the road"


UGH, those are the WORST. I have to go through one to get to one of my kids' schools. I'm always sort-of tempted to look up what the rationale for them is, since in general traffic engineers have reasons for the things they do, but then I always decide, "Nope, don't wanna open that gateway to madness."
posted by Eyebrows McGee at 8:54 PM on December 6 [1 favorite]


Ever since I started playing C:S, I irritate the hell out of everybody by going "oh look this is a SPUI! That lane there should be pushed farther back to prevent weaving! I'd replace this interchange with a turbine, but it seems the traffic is a bit asymmetric so perhaps some additional slip lanes are needed to optimise flow from the south..."
posted by destrius at 8:59 PM on December 6 [1 favorite]


“Boston's freeway system is insane. It was clearly designed by a person who had spent his childhood crashing toy trains.” ―Bill Bryson
posted by Nanukthedog at 9:54 PM on December 6 [4 favorites]


Man, I really enjoyed watching that.
posted by cortex at 10:06 PM on December 6 [1 favorite]


ok I need a smoke
posted by mazola at 10:27 PM on December 6


What about the Pittsburgh solution, which is the combination of stop signs at the end of most of the Parkway onramps, combined with the placement of a given onramp entrance just prior to the same exit's offramp, such that you have to accelerate from a dead stop to freeway speed while dodging people trying desperately to cut you off to make their exit? Then, just for kicks, do all of that 100 feet before the entrance to a tunnel.

My thought process:
"Wow, really? That's terrible design. Really?"
*Mouses around the Pittsburgh area in Google Maps, comes across the offending intersection at I-376 and Beechwood Blvd*
"Oh. Oh God."

Granted, here in Nashville, we have two fun examples on the downtown loop:
  • I-40 exit 210C at 2nd/4th Avenues, which is directly between two T-junctions for converging interstates. If you're trying to get off the exit from I-40 itself, as opposed to said converging highways, you have to blindly cross over two lanes of traffic in either direction to do it.
  • I-24 exits 47 and 48, where the south(east)bound onramp from Spring Street and the subsequent offramp for James Robertson Parkway are separated by only a few dozen meters. No tunnel, but no stop sign either. You basically just say a prayer and hit the gas. It's fun!
posted by pianoblack at 6:31 AM on December 7


I'm always sort-of tempted to look up what the rationale for them is, since in general traffic engineers have reasons for the things they do, but then I always decide, "Nope, don't wanna open that gateway to madness."

I think what it comes down to is that traffic engineers are working off models, and most of those models assume that drivers behave optimally. So things like the diverging diamond maximise flow rates (which is what the video is depicting) but completely fail to consider things like the likelihood it that someone will turn down the wrong way of an 8-lane highway.
posted by tobascodagama at 8:17 AM on December 7


What about the Pittsburgh solution, which is the combination of stop signs at the end of most of the Parkway onramps, combined with the placement of a given onramp entrance just prior to the same exit's offramp, such that you have to accelerate from a dead stop to freeway speed while dodging people trying desperately to cut you off to make their exit? Then, just for kicks, do all of that 100 feet before the entrance to a tunnel.

Jeeze, and I thought the I-95 cloverleafs north of Boston were bad.

First thing that studying Cities: Skylines road designs taught me, oddly enough, was that you should design exits and onramps literally the exact opposite of this. Exits first, then onramps. Which is basically common sense, I think? Get people off the highway to create space that people entering the highway can merge into?
posted by tobascodagama at 8:21 AM on December 7


They just put in a "Diverging Diamond" interchange along my commute, as seen at 3:20 in the video. At first I thought they had just crossed the lanes as a temporary construction measure, and then when I realized it was going to be permanent, I thought that it made zero sense as it added a couple of stoplights at the x-overs. Imagine my surprise that it actually knocked a few minutes off of my commute and works much better than the previous version.

https://www.google.com/maps/@38.8178111,-77.6391428,489m/data=!3m1!1e3 For those who want to see it in "real life".
posted by Mr. Big Business at 8:38 AM on December 7 [1 favorite]


This was intensely fascinating. It reminded me of watching Koyaanisqatsi. I need to play Cities Skylines again, like almost immediately.

Add me to the list of people who wondered whether all those drivers would be happier if they had an efficient mass transit system instead of having to travel everywhere in their cars.
posted by tallmiddleagedgeek at 8:45 AM on December 7 [1 favorite]


I think what it comes down to is that traffic engineers are working off models, and most of those models assume that drivers behave optimally. So things like the diverging diamond maximise flow rates (which is what the video is depicting) but completely fail to consider things like the likelihood it that someone will turn down the wrong way of an 8-lane highway.

My own experience is that this is, if not literally impossible, at least an extremely difficult mistake to make on one of those things. That "no no no" I cited above was indeed my reaction the first time I drove through one, because going to the oppo side fucks with your head a bit. Once I saw how it worked, I settled down, and my second time through, it was fine. The double-stoplight thing is ehhhhh, but I'm dead certain it's quicker if you're turning left onto the highway, and it seems like it's at worst a wash if you're going right or straight through. Though I don't have any data to support that.
posted by middleclasstool at 10:26 AM on December 7


Wow. I'm super happy with how this thread turned out. My son has been playing Cites:Skyline for a while now. He builds amazing, elaborate cities and traffic patterns and seems to be heading towards some sort of civil engineering future partially because of it. Me, I just liked the pretty visuals.
posted by bondcliff at 10:32 AM on December 7


The diverging diamond also has the benefit of reduced cross points where accidents can occur. So you can dump more people on to a freeway via left turn without having them turn across traffic.
posted by msbutah at 3:08 PM on December 7


I think what it comes down to is that traffic engineers are working off models, and most of those models assume that drivers behave optimally.

I never thought Cities: Skyline would make an interesting defense for self-driving cars, but there it is, in all its pristine clarity.
posted by a lungful of dragon at 12:13 AM on December 8


I think what it comes down to is that traffic engineers are working off models, and most of those models assume that drivers behave optimally.

Is that true? I used to work for a Civil Engineering firm, and they did do a lot of mathematical modelling, but they *also* were concerned with driver 'profiles'. Things I never realized were 'engineered': Distance from stop-bar at an intersection to the hanging traffic signal, The number of decision points at highway intersections (because the level of distraction for non-frequent travellers adds to likelihood of congestion accumulation).

I worked for a good, forward thinking CE firm, they refused to work in my home state because of endemic corruption. Now that I'm back home, I can tell not all Civil Engineers are that conscientious.
posted by DigDoug at 6:23 AM on December 8


First thing that studying Cities: Skylines road designs taught me, oddly enough, was that you should design exits and onramps literally the exact opposite of this. Exits first, then onramps. Which is basically common sense, I think? Get people off the highway to create space that people entering the highway can merge into?
posted by tobascodagama


It's all about cost vs efficiency tradeoffs - the phenomenon you describe is weaving, traffic entering the highway has to cross traffic trying to exit. Cloverleafs suffer from weaving but they are cheap to construct only requiring a single overhead crossing.

Contrast this to the full stack intersection at the end of the video - no weaving - but it is 4 levels high and becomes a tremendous eyesore. It's efficient but costly and ugly.

Many intersections can be a hybrid if traffic flows are asymmetrical, so you can do cloverleaf in two directions and get away with a 3 level stack.

The turbine or pinavia achieve reasonably good efficiency with only 3 levels but require all traffic to slow slightly as they navigate the curve, while in a full stack the traffic going straight does not slow.
posted by xdvesper at 2:04 AM on December 9


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