Hacker News Reader

Comment by casenmgreen | Hacker News Reader

I spent a lot of time investigating SC2K.

I came to the conclusion the game was fundamentally flawed, due to limitations in the transport simulation.

The game simulates "trips" emerging from each zone type, and a sufficient number of those trips need to reach particular other types of zone, for the origination zone to be successful.

However, at each junction, the trip randomly selection one of the routes.

So if you build, say, a round-about, or a subway system which is a loop with branches, it's death and ruin; trips have no idea where they should get off (this branch leads to industry, for example), and some trips just keep going round and round until they reach their max travel distance and fail.

You could show this issue clearly by building a square block of road tiles - each tile then having four junctions. Traffic would go into this, and never emerge.

In other words, the transport simulation is too different to real life to be playable. You had to build your transport system to fit the simulation method, if you wanted a viable city.

View on HN

Same for SimCity 2013, except the flaws extended to every agent. I've always thought that's why they limited the city size so heavily. Such a shame, because there was so much promise there.

Power, water, etc. randomly chose a direction at a junction, so even basic grid would make it impossible to power a building on the other side of the city, even if the power demand was there https://www.youtube.com/watch?v=tvq6zAMJfOU.

Traffic and pedestrians were attracted to available houses/work, but randomly every day, rather than having a defined home/work location. I built a pedestrian heavy city and would watch crowds of pedestrians head for the nearest available house on a street, before the whole street filled, and they turned around for the next nearest. Same for work, shopping, despite there being plenty available.

SC 2013 was such a let down after so much hype, for so many reasons. As a lifelong Sim-anything fan it was crushing.

Cities Skylines seems like the successor to SimCity, but even that has some deep-rooted flaws in traffic management and agent flow. Some mods exist to help coax it a bit, but it's still just a broken approach at scale.

Traffic and routing is hard, I get that, but there has to be a better way. Building a city around the routing flaws is not that much fun.

Cities Skylines can provide among the best city sim experiences to be had if you're willing to invest a day (or two) modding it to within inches of its life.

That and 32gb of RAM

Is there a list somewhere of "Essential" mods?

The CitiesSkylines subreddit has a list that contains (IMO) a good number of useful and essential mods.

Word of warning: if you're one of those people that likes to install a lot of mods keeping everything up to date and non-conflicting can be an pain the rear. There is, of course, a mod to keep track of which mods are out of date or could cause issues, but that's really a band-aid on top of a larger problem. The game is old enough now that many popular mod authors have long been abandoned their projects or otherwise moved on so you end up with things like "MyPopular Mod" and "MyPopular Mod UPTODATE" or "MyPopular Mod FORKED" or "Use this instead of MyPopular Mod".

If I take a few weeks / months between plays this usually ends up with me having to take 30 minutes to an hour to get the mods up to date and tested. Not a huge amount of time, but when your gaming time is limited it's something to take into account.

You could just... not update every time you play ?

They still add updates to the game once or twice a year, so you usually want some of the new features. That can also lead to the issue of when you finally do decide to update 3 years later or whatever, now it's a 4 hour ordeal to fix instead of 30 minutes. There's no really perfect solution, but it's worth it if you love city builders.

Steam updates the game and mods automatically. It can be overridden but that's a pain in the behind.

Can it ? In my experience, once Steam is aware that there is an update, you cannot even start the game before updating, even in offline mode... but that was some years ago, maybe this behaviour has changed ?

(Don't use Steam.)

Steam has the option to let you pin a specific version of the game if the publisher supports it, but Cities Skylines does not.

Yes, that is an annoyance. I think that Steam should put more pressure on developers to make old versions of their games available. I am glad that the software support is there (even if the UI is buried; it was originally intended to support beta–testing programs, complete with passwords to unlock the beta releases), and that developers sometimes use it, but I wish it was a formal requirement for publishing on Steam.

If you don't mind video format, I like this person's guide. He also has a 2nd video with essential mods for "advanced" players.

https://youtu.be/Nr8Wlib4jqE

He also has some fun youtube series' where he builds up a region by following a "story" he makes up (or sometimes uses viewer polls). So rather than building a super optimized city, it gets a very natural layout as he pretends to play out rivalries between developers, mayoral or policy changes, etc.

Also I seem to remember something silly involving a nuclear meltdown if you don’t have enough educated workers or if they are stuck in traffic long enough (related to the aforementioned random house issue). I wonder if there has been any fan mods to fix the issues since then. I seem to recall they eventually added an offline mode. The always online requirement was a bit excessive and plagued with issues on launch.

Are you arguing that a game in 1993 is flawed because it failed to accurately simulate a city populated with 100k+ people and associated cars and infrastructure?

I think if you assumed such a thing in the first place your premise and assumptions were massively flawed.

You're saying the game isn't playable because it was too different to real life? Did you notice the Superhero who arrives to fight natural disasters or the giant aliens who can invade? Or the fact that you can magically position fire "trucks" where you want instantly?

The flaw isn't that it is not realistic enough, but that it goes too much against an average human's preconception of how a basic traffic system should work.

It is absolutely not unreasonable to expect a 1993 game to not choose a random route at a junction; it should use a basic pathfinding algorithm (which were well-known, even in 1993) to choose the closest one.

Of course it is limited by performance but optimization is hardly a good counter-point to intuition in this kind of game.

What if the flawed routing simply exaggerates flaws with the way we think it should be designed?

The number one bottleneck in real traffic is intersections. Some people think optimal city design should mix zoning types at a finer level.

To your point though, we can't really demonstrate what's better when the agents are acting stupidly. I'd like to be able to learn what would work in the real world too.

Yeah, also it is not clear to me why is that so bad, so what that you have a circle line, wouldn't only a microscopic fraction of paths get stuck on it after a large number of crossroad steps ?

This game was meant to run on a 25mhz 386 and 4mb of RAM. Complex pathfinding and over-complicated sub-simulations would have drastically limited how large of a city you could build before your system just stopped working.

> You're saying the game isn't playable because it was too different to real life? Did you notice the Superhero who arrives to fight natural disasters or the giant aliens who can invade?

So, all bets are off when a fantastical element is introduced? We should no longer expect any internal consistency, and the work is entirely above critique?

Why didn't Frodo take down Sauron in his X-wing?? I saw the walking trees, so I know that anything is possible.

The answer is because we expect internal consistency. Ok, so there's a superhero in this game system. Doesn't change the fact that it's supposed to simulate traffic, and that this is one of the fundamental systems the game is built upon. Oh, it doesn't actually simulate traffic? Yes, this is a problem: it's a traffic simulation with superheros.

Why didn't Frodo take down Sauron in his X-wing?? I saw the walking trees, so I know that anything is possible.

That’s it, no more internet for me today. And I haven’t even had lunch!

> that this is one of the fundamental systems the game is built upon.

No it isn't. Traffic played basically zero part in the game and certainly didn't influence "success" or "failure." Traffic was 99% for visual effect. When I played Sim City 2000 I never put any work into optimizing for traffic and my cities were effectively "perfect" in terms of crime, life expectancy, citizen happiness etc.

I’m with you. I stopped participating in online discussions because of this very issue.

Interesting. This is similar to a common optimization in the genre of city builders with walkers, like Caesar or Pharaoh. In these games, buildings like a market or a temple spawn walkers, which walk on roads and distribute services and goods to tents and houses they walk past.

An important optimization in these games is to avoid crossroads and junctions, because walkers tend to randomly choose a direction at junctions. This would make it a coin flip which of the two roads would get food or religious services, possibly causing all kinds of chaos. One of the best layouts as far as I recall was just a big block with a circular road going around it, because this forced the walkers to walk past all buildings in the block reliably.

Exactly.

This is what you end up having to do in SC2K.

You must direct the traffic, by not offering junctions.

Heads up that the Pharaoh remake released today: https://store.steampowered.com/app/1351080/Pharaoh_A_New_Era...

Saw this. Really looking forward to checking it out for the very topics being discussed here. I love looking at how different teams implement these details. Is it just faked enough to be visually pleasing or do they really have each visual actor in the world doing the real work. :D Used to love playing with these details in the old version of Pharoah and Caesar.

So these ant-like cars were supposed to be more than just decoration?

Ultimately it was a game more than sim. Note the lack of parking lots.

Are there any SimCity-like games you would recommend? Or any comments on Cities: Skylines perhaps?

In Cities Skylines, each agent, each car actually does perform path planning. You can inspect the planned path of each car, and also follow it.

Skylines (which I liked) still has weird simulation errors. Like how many ships arrive at ports, which is an ever-changing amount and has no or little relation to the real transport demand. And the amount of trains using a train line depends on the number of stations, meaning outgoing train lines always need to be connected to a single one to not overflow.

How single agents path is also weird, like how much they walk. I think I remember that homes were also not persistent?

When separating city blocks completely fires would not get extinguished. Either the fire station assigned is random, or only a few actually can send cars out. Which breaks down in a city not fully connected by streets.

Haven't played for a few years now (last run was with the industries dlc), but also haven't read about patches adressing such issues.

I ultimately gave up on skylines because I kind of broke my city and it got really tiresome to try and repair or start over. Tried a few mods to greater or lesser success but they just revealed other flaws. For example, whichever mod allowed for more realistic population densities; you'd have 700 families in a residential building or w/e, but no clue where they work, and likewise in the reverse. I somehow can't click on an office tower and see what the geographic distribution of occupants is, only those that are currently commuting. I'd also get strange issues like some of my subway lines inexplicably being totally vacant no matter what I did. It's also an incredibly inefficient game to run.

Most of the agents in a building are not actually doing anything most of the time; the game has a strict limit of 16,383 moving and 32,767 parked vehicles. These numbers were chosen so that the minimum spec computer at time of the initial release would get 60fps. Mods can increase this somewhat, which is usually safe because our computers have gotten faster.

The built–in tools are also somewhat hit and miss, and that is partly driven by what information the game holds on to and what it throws away for increased efficiency. Agents know their destination and chosen route, but they don’t remember where they are coming from. Thus, when you click on a building to show the associated traffic routes it can only show routes with that building as a destination.

The exception is service buildings like fire or police; each one supplies a fixed number of vehicles, and in theory the tool could show what all of those vehicles are doing. It still just shows the routes that end at the building though, so you end up seeing just those service vehicles that are going home and people who are going to work at the service building. In principle, mods can fix some of these oversights. I use one that shows what each service vehicle is doing, for example. Another mod that I really like allows you to select a stop on a mass–transit vehicle route (a bus stop or a metro station or a ferry station or whatever) and see where everyone who is currently waiting at that stop is going. Very useful.

That said, I think Cities: Skylines is the best SimCity we’ve ever had. It is everything that SimCity 2013 should have been. I recommend it to everyone, but especially people who ever enjoyed a game of SimCity, or has enjoyed any city builder of any stripe, or who think that games are only for children.

The realistic density mod is one of the most game changing and I wouldn’t recommend it until you’re very familiar with the game and how it works/models.

Biffa has some good videos on traffic solving: https://m.youtube.com/channel/UCYzO4HZxgXc2UJQD5bIo8AQ

It works somewhat realistically but you have to learn the limitations of the simulator if you want mass transit besides busses used well.

Oh cool, added a few videos to my watch later. I just felt like I wanted more information that would be hacky to try and get

Biffa’s great if a bit too addicted to the roundabout.

I also really liked CityPlannerPlays - quite educational but more on actual city design.

https://youtube.com/@CityPlannerPlays

Most of the population just is not simulated, I think. So the game can't show you that information.

I had a similar reaction, after a city of mine completely broke because of simulation errors I gave up on it for a while. Then revisited a bit later to write an article about all the dlcs. It felt a lot more stable then, but that might be because I did not test the edge cases again.

I tried playing it again recently with mods and kept on running into issues where there would be long traffic jams on a single lane of a multi lane road. Basically it seemed like everyone had an affinity to make the same left turn at a this one particular intersection.

In a real city people would just drive around that madness and make a left turn at the next block.

Biffa has videos on “lane control” which are things you can do with mods to help reduce the single lane issues. It can be worked around but it’s not entirely realistic (there are mods that to try).

Cities: Skylines is great, but I do feel it leans a bit too strongly on the agent simulation. So much that a lot of the game is about traffic planning. You are almost required to mod the game (with TMPE) to make the most optimal traffic network, which involves manually planning each major intersection, micromanaging road lanes and configuring timed traffic lights. I've had a lot of fun with it, but I wish I could let the computer handle all the road planning details and I could get on with designing the city, but past a certain size, I feel it forces me to start doing road planning more than city planning. Almost wish there was a "Traffic Manager AI" mod to do all that for me.

Alternatively, you could use it to build dioramas. With enough mods it is one of the best tools for building digital city dioramas and best of all, the simulation still mostly works, so you get to watch people live in the city.

Overall definitely a fun game, lets you build much more natural-looking cities than Sim City, with the only downside being that the road network has a greater impact on the simulation and requires more micromanaging than I would like.

Traffic planning is the single most important aspect of planning real cities too. If everyone would just pick a spot and stay there, cities would be a lot more pleasant.

Openttd-can download for free on Steam. Works great on a mac!

Me? no, no clue :-)

https://youtu.be/NTJQTc-TqpU

Someone that spent years building an optimized city. Six million residences.

Can you explain this a little bit more? Are you saying that the game actually simulates each vehicle trip individually, and then decides on a random path at every intersection?

Mmm. The simulation engine as part of simulation any given zone, produces "trips" (I don't know how many or how often) from each zone, and figures out where those trips end up - successfully reached a useful destination, went too far and gave up, etc.

In SC2K the graphics do not depict individual cars or people, and I have no idea if in later games there is a correlation between individual cars and people and "trips" (or if trips are still used as mechanism in later versions - although from what people are writing, it seems they are).

RollerCoaster Tycoon does the same, guests wander aimlessly around park and interact with whatever they come across while considering their needs.

The Sims displays the other end of this spectrum, where agents path deliberately (while still considering their needs), and the difference in simulation scale is immense.

Simple fact is, pathfinding is a performance bottleneck that hasn't been solved yet. We are still using algorithms from the 1960s, and no hardware acceleration exists.

SimCity has always been more of a spreadsheet with houses on top.

>Simple fact is, pathfinding is a performance bottleneck that hasn't been solved yet.

But we got thousand times faster CPUs than at Sim City 2000 times.

And they have multiple cores. And if that is not enough there are GPUs with even more compute.

and better algorithms

But that still doesn't change the fact that path finding must necessarily occupy a larger and larger fraction of the cpu time as the player builds a larger and larger city. Each path becomes longer, there are more paths to plan, etc. In order to maintain an acceptable frame rate in a large city on the minimum spec computer at the time of release, Cities: Skylines has a fixed limit of 16k moving vehicles. This caps the time spent path finding as well as maximum frame time because once the vehicle limit is hit, agents start teleporting rather than being forced to traverse the map.

> no hardware acceleration exists

I'm picturing an alternate history where in addition to dedicated graphics cards, we also start building dedicated common algorithm cards - NVidia and AMD duking it out over whose hardware-accelerated sorting implementation performs best, Phoronix benchmarking how each companies' Linux drivers handle A* etc :)

GPUs are that card given the GPGPU craze in days past.

You're not wrong, but the idea of a sort of alt-history of various acceleration cards really tickled me :)

You can do a lot of shortcuts with the pathing, because you are doing a lot of pathing on a graph that doesn't change much from frame-to-frame.

Exactly. The only time you should be calculating paths is after the player places new roads. Repeatedly calculating paths on a fixed graph is a huge waste of time!

It’s even easier than that since each agent only needs to plans a path once, when they start their trip. After that they are simply following a cached path, removing road segments from it as they go. Most games will simply not recalculate those paths when you change the network, because it causes a lag spike every time the player makes a change, and because most routes wouldn’t end up changing. Better to just have cars ignore roads that didn’t exist when they departed, and have them vanish if they need to take a road that has since been deleted.

My graph is changing a lot, my whole environment from walls to objects is destructable and contains complex logic like access controlled doors.

Maybe your game doesn't change much. Lack of good pathfinding is what's constricting that the most. If good pathfinding existed, games in general could become more dynamic.

You could look into whether good-enough approximations exist?

Especially if the moving entities in your game aren't supposed to be omniscient. They could gradually learn about what good enough paths are.

I suspect pre-generation caching, game design, multi-core, SIMD versions of algs, etc. have evolved a lot.

Real-world performance isn't that determined by the form of the time-complexity.

Between Dwarf Fortress and Factorio's ability to simulate huge numbers of agents, I'm not convinced.

At least in the original simcity, as a path was made it was pushed to a stack. If the route didn't reach a destination, the stack was popped and intersections tried again. At least that's what I get from these https://lively-web.org/users/Dan/uploads/SimCityReverseDiagr... Was this changed in 2k?

The original SimCity has (IIRC) checks to see if services were available and ways to estimate traffic load, later ones tried to simulate actual trips.

So it went from “can this house reach a job” to “simulate this house driving to work” - the difference comes from a high density doing one check to doing multiple.

Does the city really get influenced by what junction a car or person would take? Weren't these objects just for visuals?

In SC2K, you do not see cars or people.

I do not know if in the later versions, there is a correlation between visually depicted cars/people and trips (or if trips are used at all, although from what people are writing here, it seems they are).

You do see a representation of the traffic, but yeah definitely not individual vehicles

Sounds like art imitating life.

Reply on news.ycombinator.com