Why I think garbage is rubbish

Some observations on garbage collection mechanics and why they cause so many problems.

Rubbish Garbage

We all know intuitively that something isn't quite right with the garbage collection in Cities Skylines. Many people with well-built, highly functional and well-engineered cities suffer from garbage collection problems. The amount of garbage dumps, incinerators and the colossal amount of traffic generated by garbage trucks is utterly disproportionate to the rest of the game. in most of my games, for the majority of game time my largest service spend is on garbage collection. I spend more on emptying bins than I don on educating my kids or protecting the streets. It's madness.

But there's no point in crying "bug" when something doesn't work as expected, we have to test it, right?

Well here's what I found.

Root causes

There are a number of elements than can easily effect our garbage collection. Some of them are entirely our fault, some are choices in the game mechanics that can be easily changed and easily overcome and others are ... well ... we'll see in this test.

Traffic. Ah yes, the beloved traffic. If you have an otherwise healthy town and start to see bin signs everywhere then this is your best early indicator that you have bad traffic. That's how sensitive garbage collection is to traffic. You garbage facilities need to get to everyone and in bad traffic, they won't be able to and people will start to complain. I'm not going to say any more on the subject here other than fix it if that seems to be your problem.

Limited intelligence. It's sad to say but hey have none. Garbage trucks make no sense in whose garbage they choose to collect.

Production / Capacity. Which ever is the problem, production of garbage far, far outweighs capacity and is horrendously imbalanced.

Location / Pathfinding. Because the bin lorries do their rounds without stopping, they don't turn round. Ever. And so this, combined with the location of your dump/incinerator can mean they can take really long routes to do simple jobs. More on this later.

Area of effect / Coverage. There is clearly no cooperation between sites in this game: they are not aware of one another and there is no one person (or code unit) responsible for overall garbage collection. I will illustrate this point with some pretty pictures further down the page.

Emptying mechanics. There is so much wrong here it requires its own section ;-)

Throughput of incinerators Put simply, it can't keep up. Not by a loooooong way. Incinerators are utterly useless. This I will show later too.

A number of these problems are deeply intertwined so please bear with me if this all seems a little mixed up and I jump around a bit ;-)

Limited intelligence.

Here is a lonely garbage truck on its way to collect garbage from a distant street in a distant corner of a residential estate.

One thing to notice is that there are four bin icons at present, two on the left and two on the right. As the truck collects the first lot of bins, an additional icon appears on the same side of the road ... but then the truck simply drives straight on by and ignores it. Why would it do that? Was it full after one house? Something strange is going on here.

So having driven up this street, the truck gets to the end of the rows of houses with four bin icons still flashing!

Let's look at this in some more detail. Here's another example of a truck going up the same street. Most of the street is now empty so these guys with flashing bin icons should get their bins emptied, right?

You'd think so but watch what happens here. Pay particular attention to the colour of the houses in this street. The colour represents the amount of garbage which has accumulated. I'm just gonna run these in sequence but also in full-page size so you can see the progression clearly. Note the first four houses are a nice, clean cyan then there's the dirty brown and orange houses further up the street in desperate need of having their bins collected.







Double-U Tee Eff. I don't need to spell out what's happening here because you have eyes and unless you've already witnessed this yourself in detail, you are now staring at your screen in disbelief. Get the full houses you spanner! There were 6 houses flashing the bin icon when the lorry went up and by those calculations they could all have fitted in one lorry but nooooo, the truck "emptied" the four empty houses first and left the full houses at the end. Noob.

Truck Capacity

Think about the implications of this. This is the very lowest level of low density residential housing. Yes, I understand that higher level houses produce garbage less quickly but still this is nothing compared to high density housing. These rows of houses in this demo town are only 30 squares long and one garbage truck, at 1% full gets through the first - let's not forget already cyan! - four houses and is already at 49% full :-\ I say again. Double-U Tee Eff. Four houses without any garbage half-fills an empty garbage truck. Uh-huh. This is what the street looks like when the truck has filled itself and moved on.



So that's what, ten houses? Firstly, the maths doesn't add up. 4 empty houses = 49% full. Move on past three more medium-filled houses and three FULL houses and that's the final 51%? Madness, I say. Secondly, ten houses!?. Good heavens. A single garbage truck of the size depicted in this game can carry around ten to twenty thousand litres of garbage. And that's compacted. A small compacting bin lorry can carry 5000 litres so what is going on here? Are we to believe that this lorry collected a thousand litres of compacted rubbish from each house on average? Come oooon. Really? A cubic metre of compacted rubbish per household, per collection on average? Methinks someone accidentally added a zero where they shouldn't ;-) A standard modern wheelie-bin carries 240l of un-compacted household waste. Your average household creates around 1 per week. I'm gonna take a guess and say that household rubbish compacts to around 20% of its initial volume when compacted under tonnes of pressure in the back of a compacting bin lorry. That means that this 1000 litres per household is probably more like 5000 litres per household or around ... 20 bins. 20 wheelie bins per household per collection. Even if it's half that - ten wheelie bins per collection per household.

This is madness. :-D

Let's do a quick test to see what a single street produces according to the game engine: If you draw a single road, 30 blocks long and fill it with low density residential, it will settle out at around 2500 units of garbage production per week which means they should only need a visit once every 8 weeks and a single truck could empty the street. That also means that according to the game stats, your average household is producing around 150kg of waste per week which is nothing like what we are observing in these collections.

Needless to say, I think that the numbers behind garbage production are severely screwed up somewhere. More testing will hopefully help us to find out where ...

So what happened in industrial areas? Something very similar. Here's our one percenter:

Who is then 32% full after "emptying" the first two empty buildings and then 68% after emptying the next two full nearly-full ones.

And is then ever-so-nearly full afer emptying ... what? Who knows then magically the last 4% clears a few more buildings.


So it seems we're using the same "oh sod it, I'll just keep collecting from the same properties" logic as the residential zones.

But did you notice the other guy? Just take note of the colour of the buildings in the next street along...

And when a garbage truck gets to the end? Remember this is only a single-sided street. There's hardly anything to collect and this truck achieves nothing. Nothing. It turns six very-nearly cyan buildings cyan and does absolutely nothing about the two buildings at the end with garbage piling up so deep they can't get through the front door.


Yeah yeah, but why is this in the capacity section? I did say I would jump around a bit ;-) The reason is that one truck managed to "empty" ten ,small family homes. The same truck managed to empty 8 factories. Both filled it. Uh-huh. So there you have it folks, in this simulation, a single-family household produces 80% as much waste as a large factory.

Perhaps a little balancing is required there ;-)

Location and pathfinding.

So what about where your dump is and how the trucks travel to and from them? There is one crucial aspect of how the trucks operate which is key to understanding how they will behave when they do their rounds. Garbage trucks only drive by properties and take their garbage and so as such, they behave like "normal" traffic. This means they don't U-Turn in the middle of a road. When they've filled their truck, they will not always take the shortest route back to their place of origin but will sometimes have to take a somewhat circuitous route. This is most apparent when you have long roads without junctions and no dead-ends in which a truck could turn around.

The example in the previous section showed our garbage truck driving up our little residential street to collect the garbage. What we didn't see is what happened afterwards. The truck was 100% full and so needed to return to the depot to empty itself. Whereas a real truck at this point might reverse onto the pavement and turn around, our simulated trucks do no such thing. They cannot U-Turn and so will continue up the road until they find somewhere to turn around. And if that happens to be rather a long road they will keep on going ... and going ... and going. In this example I joined the housing street up to the highway junction at the edge of the map. The truck is routed to go the whole way then even join the highway and come back to town! :-D



Can't they just turn around? I'm not a fan of allowing vehicles to simply U-Turn wherever they like. I'm not even a fan of having vehicles U-Turn at traffic lights as I've heard some reasonably suggest. I watch delivery trucks and they "enter" their destination and turn around as they back out. They actually pull of a manoeuvre most truck drivers would be proud of and head back off in the other direction. Someone has clearly thought about this and provided not only a mechanic but a fancy animation to allow it. It can't be a such a stretch to use a similar mechanic for garbage trucks. :-)

Area of effect, coverage and site cooperation.

How does the area of effect, i.e. coverage of a site and site and its cooperation, or lack of, with other sites effect the efficacy of garbage collection? In terms of providing efficient coverage in a city-wide collection service, I'd say a lot. You can take all the care you like in strategically placing garbage dumps and incinerators but it won't make a scrap of difference. It's a bit like schools inasmuch as the area of effect of the service seems to be city-wide and independent of the location of the service provider.

Here's a few examples of the kind of things I'm talking about :-)

Exhibit a) a shining example of a well-covered city with an extremely efficient garbage collection service, nobody complaining of garbage, wonderful transport infrastructure, nice parks and ... woah there Bessie, how much are you spending on garbage collection?!?!




The only thing that tops it is health because the garbage trucks hearses seem to use all the same logic and follow the same rules, as I'll discuss later and garbage dumps cemetaries and incinerators crematoria are a bit on the borked side too - but more on that later.

So let's take a closer look at this 'ere city. What's going on in this wonderfully efficient city and why has it taken what can frankly only be described as the spamming on garbage services to get to this stage? All we have to do here is to use the wonderfully useful Traffic Report Tool and point it at our garbage depots:

This is an incinerator at the bottom of the valley servicing an estate on the very top of the hill with two incinerators within a few hundred metres.

Another part of that same hilltop estate is being covered by an incinerator again at the bottom of the valley.


It's worth noting that the two incinerators on the hilltop estate are both operating with 4-6 trucks at any one time. If they have so much spare capacity then why are trucks being called from miles away to attend "their" estate?

And these are not isolated incidents. Below I have mapped out a snapshot in time of who is operating where and what their originating garbage depot is:


Clearly depots are operating absolutely miles away from their own sphere of influence and operating in areas that make no sense because depots with lots of spare capacity are much, much closer to the areas being serviced. Scale up the above scenario to a larger city with a larger population and a less optimised traffic infrastructure. Mayhem. :-\

This also extends to the choice of site when a landfill empties. Consider this placement of a landfill with an incinerator right next door. the incinerator is set to empty so where does it empty? Why, the other side of town of course! :-D

Landfill emptying mechanics.

This one's weird. Unless you have a tonne of capacity and "get lucky" with the game's algorithms, you can get really, really shafted by landfills filling and then consequently emptying and incinerators absolutely cannot help you.

Observe :-)

We're back in the test town and garbage has started to pile up everywhere. Due to many of the mechanics already discussed, two landfills and 40 garbage trucks cannot keep up with the production of rubbish in this town.


Let's study the effect that emptying one of the landfills will have on this little play-town.



And off goes the first truck to empty landfill a into landfill b.



He gets almost to the gate with 100% then magically has 0% a metre later. The truck doesn't stop.



And because the trucks don't treat dropping off a load any differently from picking one up, the truck won't turn around and we have the irritating little issue that they will continue on for ever until they find a place to turn.



And you end up with a long road full of trucks. The landfill is next door and they're taking ages to do a single drop. This is where the pathfinding is a real kicker and hurts. this job takes a lot longer than it ought to. Now obviously it's really easy to overcome this: build your depots on small side streeets or put small side streets either side so the trucks can turn around but that's kinda not the point, I think :-)

So let's fast-forward whilst the dump empties next door. But oh wait - what the ... what is going on?



Oh yea gods, both landfill 1 and landfill 2 are now full and are "emptying". Oops!



Oh sh... that's zero trucks in use now! And before you know it ...



notice that dump 1 is only 22% full and dump 2, having just become "full" is at 96%. that means we have a total, city-wide capacity of, what, 41% in total available? And yet we have zero trucks working. How about stop emptying landfill a and get out there collecting rubbish! :-D

Incinerator capacity

So I hear you - "you'd never do that in real life, you'd have an incinerator so the rubbish actually gets consumed". So let's wind back the clock and run the sim again with an incinerator this time. So landfill 1 is 69% full and landfill 2 is only 18% full and now we have an incinerator. We're gonna own this rubbish, right? And let's not forget we have an additional 27 trucks from the incinerator plant so yeah ... how hard can it be?



Nooooo, it's emptying to the landfill again! Why? What are landfill 2 and the incinerator up to then? Well just out collecting, it would seem.



Then literally within a minute of gameplay ...



The incinerator is full and not deploying vehicles. Oh crap, what are the other two doing? Dump 1 got to 18% before dump 2 filled up to 93% and started emptying.



And that's that. now only 2 trucks are running and everything is full. That's asking for a zombie apocalypse right there. So let's try with 2 incinerators! yeah burn that rubbish!



And so the trucks head out from the now-full dumps 1 and 2 ...




And yes, they're both emptying to the incinerator. Yay!



So far so good except, yes you guessed it. The new one is full in seconds!



Now we have 4 facilities and let's count the trucks:




2 trucks. From a total of 94. TWO. All because one landfill started to empty. It's a nasty cascade effect that can very quickly catch up with you. And before you know it: zombies.



So why does this happen? Surely two landfills and two incinerators could cope? Sadly not, not if you take into account the utter ineptitude of the incinerators. If you watch a garbage truck empty at a site, they drop off 20,000 units of trash - about right if that's litres. That means that we really are dealing with streetfulls of wheelie bins per collection per household :-D Not only that but consider this: given that an incinerator plant has a processing rate of about 48,000 units per week ...

An incinerator plant has a consumption of two full trucks per week.

Seriously what's up with that? if you don't run landfills, you need one incinerator for every twenty households at that rate :-\ The maths is quite easy to do but I reckon a single incinerator would take over 7 years to incinerate a full landfill that started emptying to it. Seven years. And that's assuming they don't collect any of their own rubbish. Which they will. So basically the ONLY answer to a full landfill is ... to build another landfill. Never, ever, ever empty one unless you absolutely have to bulldoze it for the land. Emptying a landfill will completely destroy your garbage infrastructure guys.

And d'you want to know something else interesting and seemingly daft about incinerators? They only run at full capacity when they're half full or over :-\ Whaaat. Their actual incineration rate scales with the amount of garbage they have in store. Not the amount they're receiving per week but the amount they have in store. So if you place a new incinerator, it will fanny around for a while until the problem has gotten out of hand then it'll finally be working at full capacity. Go figure. 50k units per week but my single incinerator won't even try to meet that demand until it is half full....



What's funnier, whilst testing this, I set up this city with almost precisely 48000 units of garbage production per week to balance against an incinerator. Then I thought - how do I test if a fresh incinerator would cope with a demand of 48k a week? I figured I could do that by deleting the current incinerator and placing a fresh one. Which I did. And promptly deleted 250k units of trash :-D Now that's efficient.

The real world vs the game

Maybe the idea that it would take 7 years to empty a landfill isn't such madness after all? Maybe the team at Colossal Order did their research and found these figures to be accurate. Let's find out.

The average person in the EU (is there even such a thing?) generates 492kg of waste per year. on average, 42% of that is recycled (sadly we have no game mechanic to replicate that) and 34% is shoved in the ground in landfill and 24% is incinerated.

The average household in the game is having 2000 litres or roughly 2 tonnes collected every time a truck goes past. now on closer inspection of multiple passes of multiple trucks, it seems like each household is producing enough garbage to fill a truck by roughly 1% per day that has passed since the last visit. it's not easy to follow and I'm sure someone who can delve into the code can find out for sure what each residential building etc is generating but 1% a day is easy enough to work with. It equates to 20kg per day. That would be around 7 tonnes per year and even given a massive margin for error in my observations of what constitutes a daily creation, we're still miles out. Now I do remember that the devs mentioned something about choosing to equate a CIM to roughly 6 people for the sake of accurate simulation so maybe the numbers even out somewhere under there but if that is the case, shouldn't our capacity be 6 times as much?

So what does that mean in terms of capacity etc? Well my local incinerator has an annual capacity of 200,000 tonnes which means that it is alone capable of incinerating the rubbish of 400,000 people if annual averages are used. The in-game incinerator has a capacity of 21 tonnes per week which is 1000 tonnes per year. Let me just check that again. 2 trucks is 40,000 units. A unit is about a litre and a litre isn't going to be more than a kilo so yeah - 40,000kg or 40 tonnes per ... ooooh this is off a bit. For what it's worth, my local incinerator generates 14.5MW of power, too which is fairly close to the 12MW the game has for its incinerator.

So we're let with garbage production which is many times reality, possibly due to the one-to many relationship between CIMs and people but we have an incinerator capacity hundreds of times smaller than a real-life incinerator.

I'd call that a balancing issue, right? :-)

Conclusions and some solution suggestions

Firstly, a caveat. This is all one person's limited testing, much of which has been done in a city deliberately designed to highlight problems in city engineering which has no doubt exacerbated some of the issues that have appeared. My numbers may be anomalous and not typical of a "normal" game so should be treated as an isolated case. However, I can only go on the data I have and so that is what I've done :-)

So what do I think actually needs to be done, if anything? Well, it's not for me or any individual to decide the direction of game balancing and mechanics but I would like to put forth a few suggestions I think might really help with the garbage mechanics.

Problem. It would appear that garbage trucks are assigned a route, road or block in which they are going to work and they leave to service that area. When they get there, they switch on their "collection mode" and start collecting in a linear fashion, regardless of how much rubbish is where in that zone.

Solution. Apply an "empty full properties first" approach. I believe this small tweak would really help with the overall performance of the garbage collection service.

Problem. Either households produce too much garbage or the trucks are too small.

Solution. I think that if the amount of garbage actually produced were reduced at source then this would offset the tiny capacity of the bin lorries. Perhaps if garbage production at residential properties massively reduced and industry slightly reduced then it might balance out. If one truck cannot service 100m road then something's not right ;-)

Problem. Trucks cannot U-Turn and can end up taking massive circuitous routes to do a job which would have otherwise been a simple one had they simply turned round.

Solution. Allow trucks to "end" a run once they are full and use a nearby building, or the last stop in their zone to turn around in if that provides them a quicker route back to base. the same should be applied for when the empty a landfill.

Problem. Trucks go of on crazy missions across the map to collect garbage next door to another garbage dump.

Solution. Add some sense checking into the algorithm that decides the route of a truck. If there's another depot nearer with capacity, don't go and instead send the local truck. Try to keep the trucks acting more locally whenever possible. Which is a lot of the time :-)

Problem. Landfill sites can empty across the map unnecessarily.

Solution. Similar to above, add some kind of sense-checking. Where is my closest incinerator. Does it have capacity? Use local where possible.

Problem. Incinerators are completely nerfed.

Solution. Buff them. No but really, they just don't have any use right now since they can't keep up. They have more trucks than a landfill yet they can only actually consume 2 trucks per week of garbage. After the initial fill, every landfill will only use a handful of trucks and provide almost no service to a city.

I am keen to hear other people's observations and I think it's worth opening a dialogue on how best to move forward with the garbage mechanics. As it happens, I suspect many of these "issues" are identical when you look at deahcare but I'm not gonna do that just yet. I need a rest from writing these things and I'm gonna actually play the game for a bit ;-)

So please, let's have your thoughts, observations, corrections and some good ol' conversation :-)



_Note_ I've read and re-read this a billion times now and I'm probably blind to my own mistakes and looking past spelling, grammar and non-sequiturs in droves so please feel free to point out where this doesn't make sense and I'll get it fixed :-)

[OneJasonBradly]

@Levantine, you should take that issue to the forum. For I know there are reasons for that behaviour. Search "only use two trucks" .

[Levantine]

Is this garbage issue still on going or resolved? Coz my Recycling Center have 25 Trucks, but only using 2.....

[Charlie Maxwell]

just mod the service building by giving them more range - easy fix

[OneJasonBradly]

@warrlock2001 225k you most likely are hitting the vehicle limit. 70% would cause delay in service and cause more complaints. Educated and highly educated will work everywhere at all positions.

[Merrlin]

Spot on. Reached 225,000 population and what appeared to be a garbage strike, halted my city in it's tracks. Recycling centers, incinerators with 50-100 trucks available, and waste transfer depots, only sending out 2 trucks at a time had me thinking, this has to be a bug. The game is broken. However, I'm currently looking much closer at every neighborhood road to ensure accessibility. With traffic flows at 70%, I didn't suspect that was part of the problem. I also noticed insufficient workers at these facilities which makes me wonder if my city has a shortage of uneducated workers to fill the positions for drivers.

[Some Guy]

I get wanting to add full/empty stats for every building, but part of what makes this game so playable is that some mechanics are generalised. What I mean is that I'm pretty sure stats for thousands and thousands of different buildings = the game's memory consumption would go up by 1000%

[OneJasonBradly]

Not bad possibly for a "Guide" creates one month after games release.

[OneJasonBradly]

In the first set of 9 screenshots it is claimed insultingly, "I don't need to spell out what's happening here because you have eyes" then states the garbage truck was filled by four homes. My eyes count 10 homes to fill that truck. For a garbage truck collects trash from both sides of the street at the same time on a two lane bi-directional road. Don't believe look for your self the last shot of the 9, ten homes are bright blue. They had there trash removed. And this is at the beginning of this guide.

[Queennoobi101]

Bad garbage problem in my city (24k population) YET i have a central junction with good flowing traffic! There's only one area that the central junction doesn't have a direct route to and it doesn't have any garbage problems! I have at least 1 garbage dump in those areas it connects to.What is wrong?

[Zigzagtoes]

part 2....

As for the turning around problem; due to having plenty of roundabouts in my city, I never seem to have this problem, plus I "force" trucks into areas of my city by a dedicated underground road from corners of the region tile, this ensures public vehicles dont interfere with the route beyond the area of the region they are servicing (no car will travel this far too long route to get to a neighbouring city, as it is more than twice the distance of a direct route.

As for rubbish collection, Linear is spot on, it seems from what i have observed, is that;

a. all rubbish is queued
b. rubbish is collected in order of being added to the queue
c. that list is given to a truck BEFORE it leaves the depot
d. any rubbish mounting up at other properties is therefore ignored by the truck that has just left, even if its on its route.

You are spot on too, with regards to the carry capacity of garbage trucks.