Cities: Skylines - It's all in the roundabout, stoopid

Updated: November 18, 2015

Several months ago, I discovered Cities: Skylines and fell in love with it. After so many years, SimCity 4 had a worthy successor, one that is colorful and realistic and fun and big. Really big. Not as big as it can be, but still quite awesome. Immediately, I started building some cities, failed a bit, and then hit it off with a solid, well balanced 125K urbanville.

One of the things that really came to bear during my grid-like explorations was that the square-corner, perfectly lined street design wasn't really working. All my attempts to create vivid cities with large population always ended up with massive traffic jams. I would then spend a lot of time adding more and more streets, sort of trying to fix the problem. To little avail. Then, I remembered, roundabouts.


You spin me round

Traffic circles, as they are called in the former British colonies, have a lot of real-life advantages in real-life traffic, including reducing the overall speed, simplifying and vectoring traffic, improved safety for pedestrians, less noise, and a few other perks. Not to be bested by real life, Cities: Skylines follows suit.

If you really want to master the traffic in the game, then you MUST use roundabouts. Plenty and plenty of them. Placement is crucial, and so are the ingress and egress angles of the streets connecting to the roundabouts. Too many details in one quick paragraph, let's step back, take a deep breath, elaborate and listen. That's a witty reference right there.

So, you want to have a big, successful city. This means the flow of traffic must be reasonably fast and smart. People going to work and home want to be able to do that quickly enough, without delays. Services cannot function unless they can deliver their goods in time. You also need your firemen, police, pizza delivery, and trash collection to be there when you need them. Which means your traffic network must be laid out in an efficient, friendly manner.

That sounds good, and your first two or three neighborhoods will all be tiptop. Like Turkish tells Tony, it's tiptop. You will have planned it nicely, but then your city will explode in size, and people will start moving about in an unpredictable fashion. The traffic AI is tricky, and it behaves in a rather strange way. Cars will always try to use the fastest route, and they will rarely explore alternative routes with the knowledge traffic jams could occur in certain places at certain times. This learning mechanism isn't there yet. Which means you can end up with sudden bubbles of traffic that would not happen if the game had a real, human brain.

Here's a nice little example. At first, this neighborhood only had the external square and the grid of nine roads running left and right. Soon enough, the outside roads were completely clogged with traffic. I tried to solve the problem by adding more and more connections, but that did not really do much. While the incoming traffic was more or less spread around the block, the cars trying to leave were all piling up toward the two external veins.

No roundabouts

No roundabouts, zoomed

Traffic jams

It does not look too busy, but it's all red in the graphs, and the city isn't evolving.

In the end, I was forced to cut through the hood and add two map-vertical roads, to spread some of the traffic about, but that only created additional traffic jams at the dozen plus traffic lights now created. The highway leg leading to the fourth road from the bottom is another attempt to vector the automotive stream away into the district, but that wasn't a great success. The bottleneck simply moved from the main highway arteries into the city.

A better way

My next city had roundabouts in its organic design. From the start. But again, like any decent civic engineer, I wasn't able to truly predict the traffic 10-20 years into the future. Despite my best efforts, the city footprint crawled outwards, and the roundabouts designed to handle a certain volume of cars and buses were now channeling three or four times as much, and the traffic was starting to pile up. The worst thing is, there's a compound effect to it.

Let's say your traffic layout can handle 10 cars per hour, but you have 11 cars going in. This means you'll have an extra car on the roads after 60 minutes, or as many as 24 cars lined up in a traffic jam the next day. A perfectly normal situation will have become a standstill you can only clear in three hours even if the rest of the city is frozen and waiting. This means no garbage collection, no ambulances to take care of the sick, no hearses to claim the dead. Your building may burn down, your schools won't be able to admit students. It only gets worse, and soon enough, you end up with an unmitigated catastrophe. All because of one extra car.

With roundabouts

With roundabouts, more

The original city only had the big roundabouts on the right side, the small one in the center and the one partially seen on the left. Soon enough, I was forced to adapt and carve more and more circles out of my roads, to be able to control and direct the traffic the way I needed. The grid of four almost square like roundabouts is entirely an act of desperation, designed to prevent the city from dying.

In the end, the entire neighborhood ended up carved with roundabouts, and each time, the city would flourish, more people would move in, and as the time and quality of services around the city improved, the demand also grew, and the buildings leveled up. Three birds in one stroke, or rather half a dozen well-placed roundabouts.

I was also somewhat smart enough to create different ingress and egress routes to minimize traffic jams. People coming in are guided to the nearest circle, and that included some clever juggling and digging underground highways leading from one corner of the city to the next, avoiding the urban jungle. People who want to leave have the two large elevated highways running through the city, with on ramps on every street, helping reduce the strain on the roundabouts. But it always gets tricky when you build a new district, and houses pop up, and then there's suddenly a fresh influx of traffic, and you can't really tell where people might end up going or working.

Underground roads

The tunnel connecting to the roundabout is an entirely new addition some two decades and 50K citizens later into the game. It leads all the way from the far end of the city, skips all the other junctions, and brings traffic where it's supposed to go. Think London tube. The city is now building a new express metro city end to city end system that will skip all the hundred in-between stations. Just like my Cities: Skylines example. Make sense. Reduces the strain on the central part of the system, spreads the traffic over a wider area in an even manner, improves times, and allows people to live farther away without any penalty.

Underground roads, more

The same applies to your connections from urban area to industry centers and back. Ideally, you want them far apart, like in real life, although the pollution and noise effects aren't as severe as you may think. Still, sending your laborers a few miles to work isn't such a bad idea, as it also gives you room to expand your green and blue tiles.

What you should do, if a bit of traffic starts developing, is to slow the game and then observe the flow of your vehicles. Where they are coming and from, and where they are going. This will give you a good indication whether your setup is working. If most of the traffic is merely routing through a specific roundabout and down a certain road only to get somewhere else, you can bypass that district altogether, and reduce the negative impact.


Industry wise, here's another example. Take a look at the highway. It has a bunch of connections going from one area to the other, but that means a section will always be clogged with traffic that is merely trying to get from one point to another, farther away. Redirecting it to another intersection or an overpass solves the problem. You clear up junctions and the traffic actually flows faster, benefiting your industries.

Urban industry connection

If you look at the traffic map, you will get a clearer picture of what's happening. Red parts should be a cause of alarm. Even if you do not see a problem now, it can start building up, and all too soon, you will have a disaster. This almost happened to me. The worst part was, the roundabout connecting to garbage dumps and fire houses was completely blocked, and soon enough, the city was stinky and all burning. I had to actually severe highway connections for a while, and then furiously start building fresh roundabouts to clear up the blockage. That's the chain of those almost square circles we've seen earlier. An act of wisdom and madness. Now, imagine what would happen if you didn't have sufficient funds? I like to play with unlimited money, and I'm running a fair debt, which is what most cities in real world do; pinching off the government and struggling with taxes and municipality projects and whatnot. Yup, you might as well quit and start a-fresh. Indeed, here are some traffic layouts highlighting this peril and magic:

Traffic map

Before I had the tunnel connected to the offramp on the north leg of the highway, ALL of the traffic from the northern industry district was flowing into this one roundabout, and then driving up the curved section of the six-lane road to the roundabout on the left. It was a mess. Nothing was moving. Burying some fresh tarmac under the city and its metro lines, I was able to shift some 60-70% traffic to other three roundabouts deeper in the city south, and this way, prevent the unfolding catastrophe. Now, the offramp is only used by cars and trucks that actually need to reach destinations on the far side of the diagonal highway strip. Earlier, everything, literally everything, was driving through that circle. A lesson in engineering.

Larger map

And in the industry district, the same story:

Industry connections, before Industry connections, fixed

Rather than having six roads connect to a single roundabout and cause a bit of a traffic delay, I've added another little circle just to the north of it. It's taken away some 40% traffic, and the clever placement of exit ramps helps divert traffic directly to the exit highway legs, rather than forcing them back through the roundabouts for no good purpose. This way, the traffic flows one way in, another way out, with two separate nodes to reduce the load. In the east sector, I did the same thing: created a second roundabout to disperse traffic, and create highway bypass routes so the traffic does not end up all jammed into one bottleneck. Again, exit nodes do not go through the roundabouts, and we're all one happy family. Which means growth, speed, happiness, more money, more people.

Additional improvements

More work to be done; but the addition of the second roundabout north of the original circle has already reduced the
strain on the original infrastructure by about 50%. Instead of long queues, there's just smooth, easygoing traffic. The
industry can provide its stuff on time.

The BIG upside is, once you create faster, more intelligent routes and clear up traffic, your demand will grow. Suddenly, a stagnant, flat city will have soaring requirements for new housing parcels, services and industry plots. You will seen thousands of new people swarming in. Over a period of less than a year, with no new buildings added, the overall number of people in my little village grew from 40K to 55K. All because of some well placed tunnels and roundabouts. But it gets better.


Congestion solved

Spot the difference. It's just one tiny section of the highway that does all the magic.

Here's another fine example. All of the traffic going east to west channels into a SINGLE roundabout close to the airport. But this is silly, because most of them just need to get PAST the roundabout and then hit the city bypass tunnel, as well as the northwest highway arm. So why not go around the intersection unless you need to go into the southern district? This way, the traffic flow is improved, it takes less time for trucks to ferry goods back and forth, there's increased demand for more industry, and consequently, more people. My population went up from about 60K to 65K in just about one month of game time, without adding any other infrastructure. Damn nice.

Still, there are many challenges left

It's far from over. I have recently unlocked all 25 land plots, rather than being restricted to just nine 2x2 km squares, so I will be building a million-people city. That's the plan, and that will mean a lot of time, a lot of effort, tons of luck, and some proper urban engineering. My goal is to have a huge project similar to my three-year endeavor with SimCity 4, where I ended up with 4.5 million people in some 65 districts.

Then, that's not all. Everything matters in this game. The attention to detail is uncanny. You would not believe it, but even the angle of the road and connections to your roundabouts matter. If the corners are too narrow, too sharp, the cars must slow down, and this affects the efficiency of your transportation system. The placement, the proximity, the angles, the shapes, all of it matters. It's proper bloody science. Speaking of unlocking things, mods. Yes, one of the superb parts of this game. Unlimited community modding. This is a different story altogether, and we will discuss this in a separate article.


Overview, more


More beautiful images and whatnot:

Bird view 1

Bird view 2

Image 1

Multiple cargo train stations are crucial in ferrying goods away, quickly and efficiently.

Image 2

Image 3

Image 4

Image 5


Cities: Skylines is an awesome game. And I am all the more impressed by the detail and science of it. Nothing like brutal reality to make the challenge more fun and engaging. Yes, most of it comes down to building proper roads, but then it makes sense. You can have the best schools and parks, but if no one can visit them, and if it takes four days to deliver milk or IKEA furniture, then your city will fail.

So maybe you will end up with a scattering of shoestring asphalt monstrosity all over the map, it's still amazing. You are fighting chaos, and the work will never be complete, never perfect. There's always one more alley, one more junction to figure out. It's messy, it's beautiful, and you must admit graceful defeat. The best you can do is make most of your people reasonably happy, and derive pleasure from the marred, flawed beauty of it. My little guide on traffic management may be misguided, but it comes from the heart. And having this childish joy and fascination are a sure testament to how excellent the end product is. That is, mission accomplished.


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