If you’re like me, and start having major traffic problems once you get past 20,000 population or so, then you should definitely have a look at this guide.
So this is my current baby, Victoria. 75 000 cims and growing. Not the biggest or most beautiful city by any means, but it has a delicious secret:
No traffic problems! Of course, the traffic overlay has some red spots, but…
No actual congestion, just the game telling me there’s high traffic volume, which I assume it uses to determine it’s a pretty noisy place to live. This is the first exit to the only highway access to the city.
And this is downtown, in the middle of the action. These two exits together are the main highway access for nearly 30 000 cims, and almost certainly as many jobs – not to mention Victoria U. TL;DR : no congestion, quick commutes, and (most importantly) excellent access to city services. Remember that first picture of my city? Not a single garbage dump or incinerator is in view.
The basic, textbook idea is simply three hierarchical levels of the network: local (2-lane roads), connecting (4- and 6-lanes) and regional (highways) (there’s really a fourth level, national, which in-game would be the outside connection, but we don’t build those so forget them). This organization is how pretty much all cities are built IRL.
Local roads should be where most people live; they’re basically an extension to your driveway, letting you get to the real road network. They don’t bring you anywhere themselves, other than maybe the corner store.
Connecting roads get you around the neighborhood. They’re wider, faster, and people travelling on them get higher priority at intersections than those on local roads. That said, you can still live or work on them.
Regional roads are even faster: no intersections, no driveways, high speed limit. Highways obviously fit this, but any kind of road can fit this description if built the right way, e.g. feeding the outskirts of your city with a 6-lane road with intersections hundreds of meters apart.
Here’s an example: all high-density with the only escapes the highway to the right and that one slightly orange 6-laner to the “north” and “south”. As you can see, connecting roads don’t have to be single straight lines to the regional ones, so long as their intersections are relatively far apart.
Public transit is the same idea: long, fast stretches for regional (e.g. trains and subways), buses within the neighborhood, and your cims’ own two feet to get to the door.
“But why not just make ALL the roads 4 or 6 lanes, if they’re faster and have higher volume?”
Good question, hypothetical reader! IRL the answer is style and money, the latter of which applies in-game too. More importantly though, your cims select their routes based on time-to-destination, assuming no traffic (I don’t know this for a fact, but I’m pretty confident it’s mostly true). This means they’ll tend to funnel towards the larger roads, if given the choice.
That in turn means that, as planned, the only traffic on local roads is going to be those cims who have to use them. Even with relatively long stretches of high-density development, that’s only a few sims an RL minute at the fastest speed, versus many, many more on the bigger routes.
(The following is based on 15 minutes of me watching intersections with a stopwatch).
Conveniently, intersection signals in Cities: Skylines seem to be based on detectors: they’ll stay green for the last direction to have traffic, until either ~5 seconds elapse or vehicles arrive in a conflicting lane, whichever comes first. If both roads have similar loads, that’s 50% green time for each, cutting the capacity of both in half. In the case pictured, however, over 5 minutes the 4 lane avenue got 32 seconds of green for every 5 on the local road.
I *think* you can improve that a touch more by having the local roads be alternating one-way streets. IRL, having no traffic coming in the opposite direction is a serious boost to capacity. Cims being robots, though, can drive between each other without a care in the world, and my local streets don’t have enough traffic on them either way for a serious comparison.
There’s also the issue that you need more intersections, since the services may have to travel around the block, slowing them down. Still, I like them.
Trucks! Trucks everywhere!
Of course, all of the above applies mostly to cars and commuters, who can go from anywhere to anywhere. You have to provide them with very general solutions, but you can let them do there thing once they’re almost home.
Industry is different. If you’re like me, you have it concentrated in a few areas, and while there are less trucks than cars on the roads they almost ALL take the same few routes. These routes will suffer huge volumes, potentially domino-ing to your city’s untimely demise.
Fortunately, the game provides a few very powerful solutions, unique to industry:
1) District policies
Banning heavy traffic is free, and thanks to your amazing police force 100% effective: no trucks will go through the district. Obviously, this only moves the problem, but it can push trucks out of quiet little Suburbiton and onto the specially built highway, despite it being a 6 hour detour.
Just don’t forget that cargo has to go SOMEWHERE. If you don’t provide any routes, your industries aren’t going to be happy.
2) Cargo trains
At first I thought cargo trains were only for getting goods out of or into the city. Not so! While you don’t create routes for them like you do for other transit networks, the cargo train stations will kindly figure it out themselves and bring cargo wherever it’s needed. Moreover, since cargo is far more predictable than commuters, you can quickly and cheaply build a very simple, out-of-the-way network that heavily reduces the number of trucks on the roads.
…well, on the roads that matter anyway. Cargo still has to get to and from the train stations, and no clever tricks can increase the capacity of the cargo bay itself. You can easily get long truck lines for the train station. I don’t know a real solution to this, but there’s 2 ways to reduce the problem.
First, if you’re facing the front of the station, know that trucks always enter on the right and exit on the left. Build it on a one-way road going that direction, and at least you won’t have the added problem of them yielding to each other.
Second, you can just build the train station somewhere where lines won’t bother anyone, and then hide that section when you’re showing off the low traffic in your city :/
Dem clever industries
One last thing for industry which isn’t immediately obvious: cargo can take some pretty clever and complex routes. This is a train station right next to the cargo harbor; trains bring the cargo from all around the city to the station, which then spawns trucks to drive it to the ships. The harbor does the same thing for imports.
Do note that this will create some MEAN traffic between them. I gave them a dedicated set of onramps. It would be nice if the train could offload directly to the ships, but what can you do.
Anyway, those are the overall strategies I can think of right now. I’ll end with a few…
MISCELLANEOUS TIP #1
Don’t forget that transit routes provide valuable happy faces, count as a service and increase land value. No reason to wait until you have congestion to start building them.
MISCELLANEOUS TIP #2
Ironically, buses can be a major source of congestion. Despite apparently emptying and filling up almost instantly, they wait a set amount of time at the stops, making buses behind them block up a lane while they wait. If you have a lot of lines converging in one place (say, at a subway station) try having a few adjacent bus stops for the different lines. One stop for every two lines seems to work for me.
MISCELLANEOUS TIP #3
Just as a regional road doesn’t HAVE to be a highway, long distance public transit doesn’t have to be trains or subways. I built the latter here after plopping the space elevator, but when it was just an airport I connected it to downtown (specifically, the central subway station) via a bus line with just the two stops. Each plane-load can generate up to 100 cars, and this brought that down to almost zero.
MISCELLANEOUS TIP #4
The game warns you about this in extreme cases, but don’t have intersections too close together! This avenue acts as a service road for the highway, but bends away from at the exists so as to avoid backing up traffic into the roundabout. Speaking of which…
“roundabouts are so great why aren’t you building them everywhere omg”
Roundabouts are indeed pretty sweet. To be honest, you can ignore almost everything you just read and plop roundabouts everywhere. As an added bonus, they look nice and are a central tool for ton of the amazing cities I see on this subreddit. The only downsides are that they take a little longer to build, and they take a lot more space.
Personally, I feel like relying too much on roundabouts is a lot like sticking to grid-based cities: it can definitely work, but it gets a bit repetitive to build. That said, I do use them where I need to (mostly to connect to highways) and occasionally make random ones since they’re undeniably pretty. Like everything else in this game, what you do is up to you.
Thanks for reading! This took a lot longer to write than I’d planned, so I hope it helps someone out.
Feel free to ask me any questions in comments, or PM or whatever.
Have fun building!