Traffic - Understanding and fixing early problems in your city

A guide to understanding what causes early traffic problems and how to overcome them.

Introduction

Unless you're a veteran to city building or just really good at traffic planning, you're bound to make mistakes when building your cities. We've all done it: built a great looking city block or estate and then realised that it's just not compatible with good traffic flow and we end up with nightmare gridlock and lots of frustration. If you build dense and imperfect, it's really hard to rectify problems without destroying parts of your city so it's important to plan ahead when you're building and leave room for further expansion of your road network.

In this guide, I intend to highlight some of the more common problems faced early on if you don't plan, help you to use the tools available to you to analyse the problem and show you what solutions work and what don't. And more importantly: why.

Welcome to early traffic 101

Recap

We started this city with a specific design goal in mind: to illustrate the different zones, services and their interactions with one another.


I explained how essential goods and services move around your city as follows:

Originally posted by "Me":

Raw materials come from outside your city to your industrial estates. Your factories make them into finished goods which are transported via truck to the commercial district. Goods also get exported out of your city. CIMs travel to both of these places to work. CIMs will travel to the shops to buy stuff. Note that I've used a thicker line to indicate this is more people! Your CIMs will commute to their own place of work - some will work in factories and some will work in shops. However ALL of your CIMs will want to shop. In addition to this, every zone will require services - more and more as the game progresses. These services will need access to some or all of your zones depending on the service.
This flow of people and goods is vital when considering your transport infrastructures. But more on that later, we have a city to build, right?

As you can see, we've built the city in this format and there's tonnes of traffic trying to keep up with all of these demands.

Seeing the early signs

One of the best ways to overcome traffic problems is to anticipate them and overcome them before they become a problem at all. This isn't always easy but it's an ability which grows with experience and I tend to find you city builder types learn quickly ;-)

As I was building this city, having deliberately built it with very separate zones and only a single, small connection in order to illustrate game mechanics, the main connecting road between the zones very quickly became full of traffic. However, since it was not actually stopping and causing traffic jams, I have been able to ignore it and allow the problem to grow. Flowing traffic is rarely a problem, no matter how heavy the flow. It's stationary traffic of any kind that causes problems very quickly. Look for the jams. Find them, understand them and fix them.

The first hint that traffic was getting to be a problem can be clearly seen in this picture. Whilst you can't see that traffic is flowing, albeit slowly, what you can see is that there are bin signs everywhere and two garbage dumps in the middle of the map. Two garbage dumps is 30 trucks and easily enough capacity for a city of this size with plenty of capacity to spare. But still garbage is piling up. it can only mean one thing: traffic!



These are early signs that traffic is getting from simply heavy traffic to crippling traffic. One of your services now isn't functioning properly and it is all down to heavy traffic. The garbage trucks simply cannot do their rounds quick enough to satisfy everyone.

Spotting these symptoms early can prevent disaster.

Tools of the trade

Cities Skyline comes with a great suite of tools out of the box to help you to understand what your CIMs are doing. Because every CIM is properly simulated, it makes troubleshooting much easier because you can simply see what they're doing.

CIM detail. You can click on any CIM or any vehicle at any time to find out who they are, where they're going, where they live or belong and all sorts.









Traffic Tab. Using the traffic tab, you can get a quick view of traffic volume and speed. Sadly, this tool seems to grade the colours depending on a combination of volume and speed so it's not immediately useful for finding stationary traffic. However, it quickly highlights hotspots for you to look at.


Your Eyes. Again, thanks to the fully simulated nature of Cities Skylines, you can see what is happening and where and what you see is a true representation of your CIMs, their lives and their journeys. Your eyes are your primary tool - use them! :-)

Mods

Traffic Report Tool by Black Widow. I make extensive use of this tool and it is amazing. Get it. Use it. Love it.
http://steamcommunity.com/sharedfiles/filedetails/?id=408092246

Understanding the first problem.

OK. We know traffic is now causing a problem but why? Yes, the symptom is that garbage isn't being collected but what is the route cause? What is behind this madness? "Too much traffic" is not the answer. You need more detail than that to truly understand what is going on.

Let's use some of the tools available to us to find out what's really happening and why. First, we'll use our eyes. Oh look the traffic stretches all the way between the industrial and residential zones.

So again, using our eyes, let's see whether both ends are a problem or if one end is more problematic than the other.

Looking at the industrial end of the road, the traffic is all on the left hand side (UK roads, of course) and so is leaving the industrial estate. Hmm, this obviously isn't the route cause of our problem. Why are they all backing up at the other end? Looking purely internally, CIMs need to get to work at both the factories and the shop and ALL CIMs need to shop so from a residential point of view, the highest traffic flow ought to be from the residential to the commercial districts. So let's take a look:

Can't be here. There's no jam of people trying to turn right at this junction and as you can see up the road, even though this traffic consists of both people going to work and people going to shop, it's not that significant. Let's continue down the road to see what's what.

Uh-huh. I see me a problem. There's a tonne of traffic coming in from outside the city! That traffic is mostly made up of trucks and tractors and they all want to turn right - across the flow of traffic at the end of this junction. That's not good.
There are no lights on small road junctions so it's every man for himself here and the trucks are obviously winning. So what's going on? We need more information!

First we need to find out why there's so much traffic coming into the town. Remember we previously talked about raw materials coming into your city to enable your factories to operate? Well that must be it, right? After all, we've established that it's not people going to work or people going to shop or even good being taken from the factories to the shops and service vehicles are a symptom of our problem and that's all that's left.

So let's check it out using the Goods tab in the menu. Clicking on the goods tab immediately highlights which buildings are importing goods and which vehicles are involved in this process.



Strange. Yes, a good number of factories are importing goods but that's really not a significant amount of traffic to be causing our problem. OK. What about exports? I know we're looking at a problem with incoming vehicles so that might not seem immediately intuitive but let's take a look anyway.



Well well well. There you have it. Every single industrial building is currently exporting and the vast majority of the traffic coming into the city is exporting. In fact: the vast majority of traffic on our main problematic road is in fact export traffic.



Yes indeed. A lot of export trucks! Now why, you may ask, is all my incoming traffic export vehicles? Isn't that back to front? It is until you realise the level of simulation in this game. If a vehicle leaves a factory to export goods then the simulation will show that vehicle and its journey to the edge of the map. It will then show the return journey so the same vehicle can come back to collect more goods! if you have a load of stuff leaving your city by vehicle, all of those vehicles have to return at some point in equal measure.

So there we have it, we have understood what is going wrong here: our city is being brought to a halt by a mass of export vehicles which leads us to massive conclusion and lesson number 1 when it comes to starting your city:

ALWAYS place your industrial zones next to the highway.

Fixing the first problem

OK. We know what the problem is but how do we solve it? What's the first thing most people think of when they see a traffic jam? "Build bigger roads!" Sadly that isn't going to fix our problem. We could make this a six lane avenue and you'd still have your problem that people need to get on and off the highway and we have too much traffic coming into the city. The junction simply doesn't have the capacity. However, whilst it might not solve the route cause of our problem, it will certainly help to alleviate one of our biggest symptoms thanks to the clever way drivers behave on Cities Skylines roads.

So let's get on with it and see what happens! :-) I'm going to go a single size so that we double the number of lanes available in each direction.



So looking at the industrial end of the road, widening the road to two lanes seems to have helped somewhat. Let's see why that might be. Looking down the road to the junction we can quickly see why. The cars are now using two lanes instead of one. Clicking on each of the vehicles in turn shows that there's a full mix of vehicles exporting goods, goods being taken to the shops and CIMs driving to the shops, CIMs driving home and import vehicles returning to their rightful owners. Obviously the vast majority are export vehicles but all types are using all lanes except those going to the shops (CIMs & trucks) who are all in lane 1.



What this shows us is that the junction in the middle of this road is not a bottleneck because adding extra volume didn't cause further problems and the junction had the capacity to allow the (now main) road to carry a higher volume. The Ai can see and understand this and is happy to use both lanes. So what happens further down the road?



A couple of important things are happening here. Firstly, the new addition of traffic lights to the middle junction means that cars are let up the road in small packs. This gives them the breathing space they need to be able to get into the correct lane before they reach the junction. Secondly, when a queue does form at the end of the road, the huge amount of export traffic behaves itself and queues up in the left lane since they are all going left onto the highway. this then allows local traffic heading for the residential estate to carry on their merry way and get home. It also allows our much-needed garbage trucks to whizz on by the traffic jam and get on with their jobs! Yay!



Thank goodness for considerate drivers, eh? Just imagine what would happen if everyone was impatient and used lane 2 to simply fill up the available road, trying to dive into the jam at the last minute? Gridlock.

So the first problem we saw was that garbage trucks were being impeded in their rounds so we have provided an extra lane at the main problem point to allow them to continue their rounds without sitting in a queue for hours.

Providing additional relief

Looking now at how the city settles after the introduction of the two-lane road reveals that there are still queues but they're shorter but that makes sense since the road has more capacity and multiple lanes are being used. Looking at both ends of the road, the residential end is looking much nicer now but the industrial end is still pretty heavy simply due to the road layout.. There's too many junctions, two frequently and too close together.



One thing we have now created, however, is a traffic jam in the middle of the road because there are now lights there.



We've created this problem primarily because the industrial sites need access to the highway a lot. But what else do we know about the movement of vehicles around the map? Currently, everyone is using the same road and this will soon turn into a serious problem if we don't provide some kind of relief. Here's a few things we can look at:

• Split the residential traffic so that people going to shop are not caught in the main goods traffic on the main thoroughfare.
  
• Help to get the finished goods from the industrial zone to the commercial zone more easily.
  
• Help to get the imports and exports to and from their destinations more easily.

In this map's current configuration, there is a very quick short-term fix to a couple of those issues: we provide direct link to the commercial zone from both the residential zone and the industrial zone. This should help with two of the three points above.



Simples. This has a few excellent effects. Workers working at the commercial sites now have a direct route to work. Shoppers also have the same direct route to shop from home. Also, workers at the industrial park often go home this way now and do their shopping on their way home. Goods vehicles are indeed taking their goods down this route directly from the factories to the shops. Excellent. So let's have another look where we're at. There's still a fair bit of traffic on the main thoroughfare and it's still mostly import and export vehicles.



So what can we do about it? There's always another way ;-) In this map, there are four highways connections and we're only using one. So let's use another! There's one right by the industrial zone so it seems like an obvious candidate :-)



Normally, OI would have actually extended the highway itself and made the junction closer but making a very simple, one-lane, two-way road to the highway instead helps us to demonstrate that actually, you can go a long way with very small roads. They have lots of capacity :-) The net result here is that a load of delivery trucks are now using the new relief road to export their goods. It is by no means all but more than half and it is what it was intended to be: a relief road.

Further techniques to avoid queues

What we have achieved with these few, small changes is to completely transform most of the map to a nirvana of smooth flowing traffic and no jams.

Whilst moving the problem to the industrial zone and making mayhem over there.

In fairness, the traffic is all industrial traffic so let them deal with it and we have successfully prevented this heavy goods traffic from impeding the rest of the map. Result. But we still have a traffic problem simply due to the volume of goods traffic we have to deal with. So how can we help?

Here's a few basic tips on speeding up throughput of traffic and avoiding jams:

• Avoid putting junctions near each other where possible
  
• Try to get inbound traffic to its destination without impeding the exit of outbound traffic.
  
• Try to get outbound traffic out of the city without impeding the entry of inbound traffic.
  
• Avoid crossroads at significant interchanges. They cause massive queues.
  
• Learn from nature.

Learn from nature? What are you talking about? Nature doesn't build roads. Nature actually builds roads all the time. Your lungs are roads: they are designed to get the maximum amount of gas in contact with the maximum amount of blood in the smallest possible volume. A tree is a massive two-way road. Think of a tree as a huge residential estate and a huge industrial estate. The leaves make sugars and energy which has to be distributed around the entire system whereas essential nutrients and water are imported at the roots and equally distributed throughout the entire system. The same goes for your blood: all blood goes through the heart and lungs but has to get to each cell in the body somehow. There's no surprise that biological terms are often used to describe roads (at least in English in the UK) like trunk roads and arterial roads.

Nature achieves this effectively through the use of fractals and many fractal images show the same patterns and shapes as we see in nature and it's very short leap from a fractal trees, fractal lightning, fractal rivers etc to a fractal road map.





What all of these have in common is that the capacity of the conduits/roads increases precisely with its need. Trees have leaves on tiny branches which sprout from thicker branches which have in turn sprouted from thick boughs which come from the main trunk. Each gets thicker toward s the trunk and thinner towards the edge. River tributaries do the same thing by flowing into main river stems which in turn flow into larger rivers and eventually to the sea.

Yes, all very pretty, right, but what is the point? The point is that you should be thinking about building your road networks to mimic this kind of functionality. There's no point banging down 6 lane avenues where a single land road will do the trick. For a start, larger roads get priority over smaller roads: think about that when you're making your networks. Keep the trunk roads flowing as much as you can. If your trunk road going through a district is a 6 lane avenue but all of the tributary roads are also 6 lane avenues then you have a New York gridlock scenario full of horrendously inefficient interchanges. Scale in increments and only use roads you need.

Enough about nature - what can we do about the other points? Two things: one way roads and roundabouts :-D With those two simple tools at your disposal, you can direct traffic where you want it to go in order to keep it moving. Let's have a play on our map to see what happens in some of these scenarios.

Putting it into practice

This is the current flow of traffic:

What would happen if we turned our main industrial roads into a large one-way system?

What we can see here is that this suddenly makes the traffic move much more freely since they're all going in the same direction. Traffic is still really busy though. SO let's have a look and see what a roundabout does to a system like this instead of a one way.

Plus points and bad points. There's a lot less traffic on the actual estate now but the roundabout is very busy and there's still a queue trying to get onto the roundabout from the north where all of the import/export traffic is going. So what can we do about this?

How about combining the two?

Now we're getting somewhere! Free flowing traffic with only brief queues when tonnes of trucks arrive. You'll notice that I've effectively split the entrance and exits to the east and west sides of the estate using separate one-way small roads. You can achieve exactly the same effect using a dual carriageway (4 lane road)if you like. What is worth illustrating here is the organic and fractal principals have proven themselves to be effective. Whilst it may not, at first, seem like we have just built an organic road system, our focal point, the roundabout has 3 lanes of traffic: that is the trunk. We then have a load of one-way single lane roads which provide 2 lanes of traffic: these are the boughs. We then have the two-way single lane roads on which the industrial buildings are actually built which provide a single lane of traffic: these are our branches and the buildings are our leaves.

Conclusions

What I hope we have learned in this little exercise is that it is always better to understand your situation and provide surgical changes to overcome your root cause than it is to simply throw lanes at your traffic. if we have converted every single road in the city to a 6 lane avenue, we would not have fixed anything. However, since we investigated the problem, we were able to discover that the root cause of our traffic woes was a whole load of export traffic. This traffic was significant enough that crossing the city meant bringing the city to a standstill and it was also blocking up the industrial estate.

So what did we do?

We provided an extra lane for right-turning traffic entering the residential estate. This freed up local traffic to go about its business unimpeded by the export traffic.

We provided alternate routes for traffic going to and coming from the commercial zone. This allowed workers, shoppers and goods vehicles a direct route to fulfil their needs.

We provided an alternative route to the highway for export traffic. This more than halved the heavy goods traffic crossing the city to the original highway junction.

We provided a new junction layout on the industrial estate. This allowed traffic to enter and leave the industrial estate with much more freedom and greatly sped up the flow of traffic around the estate itself, almost entirely eliminating queues.

Applying the basic principals of traffic building and using nature as our guide, it's not that hard to build an efficient traffic infrastructure. When you're building early on, try to remember some of these changes you're likely to want to make before you get to 10,000 CIMs and leave room for them if you can. Don't be afraid to destroy growable buildings to make way for infrastructure; as long as you have demand, they'll come back.

I hope this has been informative and I hope I've managed to communicate my points clearly - do tell if not ;-)

Happy road building :-)

[Toxic]

I'm not playing this game too much infos haha

[Oshidashi]

The comparison with structures in nature elevates this guide from nerd porn to a great read.

[Mina Miko]

this is a really great guide yet i feel like im not fully grasping what its explaining :(

[mgeo17]

I've considered budgeting my garbage collection and deathcare services to operate mostly at night, using the individual day/night sliders on the city budget panel. Have others found this to an effective solution to minimize peak traffic and co-mingling between services, trucks, cars?

[STS]

This is really informative. Thanks

[christian.vansomeren]

Great overview, thanks!

[Crast™]

Why is the text overlapping the images?

[Tritoch]

The first traffic guide that made any kind of sense to me. Thank you!

[sunscreemer]

You should be a city traffic planner- very smart tips, thanks.

[Starwink]

You had me at fractals! I'm always trying to use that logic when making my transport system. My current city has 40 000 citizens and minimum traffic problems for now. The part with map an exports was very interesting, will use it to see how my city can be improved. thanks a lot for your smart article