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NAM Traffic Simulator Development and Theory

Started by z, August 02, 2008, 05:07:50 PM

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woodb3kmaster

I look forward to testing the new version of Z Medium! I'm hopeful that it will eliminate (or at least minimize) my continuing problem with no-job zots, as merely removing the no-abandonment mods I was using has so far proven ineffective.

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z

When you get your no-job zots, which I assume are followed by abandonment, is the abandonment due to commute time or demand?

woodb3kmaster

The abandonment is always due to commute time. It would be strange to me if it were due to low demand, as the residential demand levels are all pretty high (at least from a non-CAM point of view).

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sumwonyuno

I just loaded the backup copy of Capitalis and my plugin folder, and replaced the Simulator to 2.0.  I can say I'm pleased with the results.  Commuters in signficant numbers are actually using King and Beretania (major east-west one-way throughfares) in the Downtown city tile.  The disproportional pedestrian levels are more in line to what I think is much more reasonable (a bit higher than bus usage, rather than half the number of cars).


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z

Quote from: woodb3kmaster on December 16, 2009, 08:06:38 PM
The abandonment is always due to commute time. It would be strange to me if it were due to low demand, as the residential demand levels are all pretty high (at least from a non-CAM point of view).

In that case, I would expect that the new version of Simulator Z would at least reduce this abandonment.  Please let us know what you find.

Quote from: sumwonyuno on December 16, 2009, 08:29:12 PM
Commuters in signficant numbers are actually using King and Beretania (major east-west one-way throughfares) in the Downtown city tile.

I'm very glad to hear that the changes to one-way roads are helping here.  I'll be interested in hearing from other people on this as well.

QuoteThe disproportional pedestrian levels are more in line to what I think is much more reasonable (a bit higher than bus usage, rather than half the number of cars).

A bit higher than bus usage sounds quite reasonable, as Sims have to walk to get to bus stops.

woodb3kmaster

After an initial eight-year playing session in my largest city, I have found that the new version of Simulator Z has not helped in any measurable way. Abandonment continues in the north-central part of the quad on an approximately 9-month cycle. I'd be happy to provide any further information you need in solving this problem.

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z

You mentioned that you used to have no-abandonment mods installed; do you have any other game mods installed, such as ones that boost demand?  Also, do you have sufficient jobs for the residential wealth types that are abandoning?  (You need to use the Route Query Tool on a building to find the actual number of jobs filled; Sims that arrive by multiple means of transportation are counted multiple times.)  Finally, assuming they exist, about how far away are these jobs from the abandoning residences, and what is th customer level of their buildings?

z

After thinking about woodb3kmaster's situation, I decided to do some more testing of my own.  As I mentioned earlier, the v2.0 release of Simulator Z eliminated abandonment due to commute time in all my cities but one.  However, this city, with a population of 1.16 million, still had a fair amount of abandonment in one area, and was not as healthy as the other cities.  I think that there's an excellent chance that what woodb3kmaster is experiencing is essentially what I was experiencing in this city (Logan Square).  The good news is that the problem does not seem to be due to the traffic simulator, and furthermore, the problem appears to be fixable without changing the layout of the city.

First, I tried tweaking various parameters in the traffic simulator to see if I could at least reduce the abandonment.  Nothing helped.  I also tried other traffic simulators, most notably Simulator E (5x version), which has perfect pathfinding and is the Maxis-based simulator closest to Simulator Z.  Once again, the results were unchanged.

This led me to a fundamental question:  Why was this city behaving differently from all my others?  The most obvious difference between this city and others in my region was that this city did not use subways, whereas others did.  There were certainly enough jobs in this city; the abandonment was happening in the southwest quadrant, but at the extreme northeast corner of the city, there was a Velacosma tower that had grown long ago, and half its jobs (about 11,000) were open.  Why weren't the Sims getting to them?  A route query on the Velacosma showed that Sims were commuting to it only from about a third of the city tile.  In fact, there seemed to be a straight line, beyond which Sims would not commute to this building.  I have seen this line in other contexts, and it seems to be an artifact of the destination finder's behavior.

Fortunately, I had an alternate version of this city available, which was identical to the first version except that it had an extensive subway system.  When I ran this city, there was no abandonment at all.  The Velacosma was now full up with jobs.  Interestingly, the area from which its commuters came had expanded, and was mostly by subway, but this area did not extend all the way to the area that was abandoned in the original city.

With this knowledge, I went back to the original city and put in a moderately extensive subway system.  Sure enough, that solved the problem, and the abandonment disappeared completely.  Progress was originally slow but steady.  Then I left the game for just a little too long, and I had a power crisis, leading to abandonment of 25% of the city before I caught it.  When I restored the power, the Sims quickly returned, and by the time things stabilized, all the abandonment was gone, and the Velacosma was staffed at full capacity.  Route queries showed that the city now looked very much like the version that had originally been built with subways.  Interestingly, Sims in the formerly abandoned area were all commuting to nearby jobs; none of them were commuting to the Velacosma.  The city is now completely healthy, with no abandonment.

What is the lesson here?  I had known since SC3K that large cities needed subways to function well.  I had even seen this in SC4 with Simulator Z; growth was inhibited when zones were far apart unless there was a subway system in place.  This actually didn't make sense, as with perfect pathfinding and unlimited commute time, as well as all the other tuning, Sims should always find available jobs, wherever they are in the city.  But they don't.  Once again, this appears to be a function of the destination finder.  One of the functions of the destination finder seems to be to prune down the number of possible destinations so that the pathfinder doesn't have to work so hard to find a valid path.  And one of the ways it does this, apparently, is to say that in big cities, there is a limited distance that Sims will travel without subways.  This distance appears to be hardwired into the destination finder, and is completely unrelated to and unaffected by the Commute Trip Max Time property.

This doesn't mean that you need subways for all big cities.  In the original city, if I simply zoned high density commercial near the abandoned area, skyscrapers would immediately sprout, and the abandoned residences would become reoccupied quickly.  No subways were necessary.

It's also not clear whether other rapid transit, such as commuter rail or monorail, would work as well as subways.  They might, but they would require extensive changes to the landscape.  And then again, it may be that subways specifically are required.  I'd be interested in hearing from anyone who has more experience here.

My conclusion at this point is that all the abandonment I have seen with Simulator Z v2.0 is a fundamental property of the traffic simulation, but can be avoided by the addition of a sufficient subway system.  (Sufficient numbers of jobs are obviously necessary as well.)  I found no parts of Simulator Z v2.0 that needed further tuning, and in fact my experiments confirmed that this version appears to be tuned rather well.

In my next long post, I will finally get to the details of what I have found out about tuning the destination finder, and I will include what I know about tuning the pathfinder as well.  I'll also include what I have found out about how these two parts of the traffic simulator work together.

woodb3kmaster

Quote from: z on December 16, 2009, 11:05:11 PM
You mentioned that you used to have no-abandonment mods installed; do you have any other game mods installed, such as ones that boost demand?
 
I do, in fact, have a demand-altering mod, but it's an ordinance and I never use it. Might it still have some effect, despite its lack of use? I also have mods that alter the stage caps for CO and R, as well as an industry jobs quadrupler, if that helps.

QuoteAlso, do you have sufficient jobs for the residential wealth types that are abandoning?  (You need to use the Route Query Tool on a building to find the actual number of jobs filled; Sims that arrive by multiple means of transportation are counted multiple times.)
I haven't yet gone back into the game to check this out, but when I do, I'll edit this post.

QuoteFinally, assuming they exist, about how far away are these jobs from the abandoning residences, and what is th customer level of their buildings?
The highest concentration of jobs in this quad is just to the southwest of the center of the quad, while the area suffering from cyclical abandonment is in the northern fourth of the quad, mainly north-central and northeast. No other areas of the city have this problem.

Your newest post is intriguing. My quad has an extensive subway network, but most of the lines are radial, feeding into the CBD. There is only really one orbital line in the quad outside of the CBD itself. Here's my subway volume map:



Do you think that this problem might go away (or at least be greatly diminished) if I added another orbital subway line passing through the affected area of the quad?

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z

Quote from: woodb3kmaster on December 18, 2009, 04:15:06 PM
I do, in fact, have a demand-altering mod, but it's an ordinance and I never use it. Might it still have some effect, despite its lack of use?

No, though I'd recommend getting rid of it anyway, for the reasons I describe below.

QuoteI also have mods that alter the stage caps for CO and R, as well as an industry jobs quadrupler, if that helps.

This could definitely be part of your problem.  A lot of these earlier mods were made as patchwork fixes to central problems in the way the game worked.  None of them addressed the whole picture completely.  Some might fix one area, while making another area worse.  I would strongly recommend uninstalling all of these mods.

If you still have problems after this (or even if you don't), the next step would be to install CAM, which contains a really comprehensive approach to balancing supply and demand of residences and jobs.  The released version of CAM has a serious demand bug that manifests when playing more than one city; this bug has been fixed in CAM 2.0.  CAM 2.0 has not been released yet, but it is in beta, and if you posted in the CAM - General Discussions thread, I'm fairly sure RippleJet would give you access to the beta versions.  I think that CAM would help you out quite a bit.

Then, if you still have problems, the map you posted shows fairly heavy usage (100% or greater) of many subway lines.  An outer belt may help, but you may also need more lines going into your CBD.  I would add some lines, and if that helps, keep adding lines until your problem disappears.

Finally, it is very possible that you don't have enough jobs for your Sims, even though you have positive residential demand.  As a rough check, the sum of your commercial and industrial population should be about half of your residential population (i.e., your workforce).  If it's significantly less, you're short of jobs.  That may be OK if your Sims are commuting in large numbers to a neighbor city, but that doesn't appear to be the case here.  You may need to either grow your CBD, or create smaller, additional business districts elsewhere (such as near your abandoned residences).

So I see many possibilities for why you may be getting your commute time abandonment.  I think that if you try the various solutions I proposed, one or more of them should work for you.

woodb3kmaster

Here's a little update. I uninstalled those mods and added more commercial zones near the problem areas, then started running the game. Initially, everything was going well, but about 18-21 months into the playing session, the no-job zots started coming back, in the all too familiar pattern. The first cycle wasn't too bad, but the second was awful. It seemed like almost every residence in certain small areas was abandoning! About five years into the session, I added that outer subway belt I talked about earlier. That seemed to help part of the affected area, but there was still abandonment happening towards the northwest and northeast corners of the map. I stopped playing the city after ten years, at which time the abandonment cycles were still going on.

In sum, I've implemented all of your recommendations except for adding more subway lines into my CBD and getting CAM 2.0 (still waiting for an answer from Tage). I also checked my population levels and found that the job population (C only, as there's no industry in this quad) was about 54% of the residential population at the start of the test. Also, route-querying various commercial buildings revealed that there are far fewer Sims working in each building than the normal query window would have me believe.

Once I get my hands on CAM 2.0, I'll be sure to install it and run the city some more.

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z

#431
Quote from: woodb3kmaster on December 18, 2009, 11:26:30 PM
I also checked my population levels and found that the job population (C only, as there's no industry in this quad) was about 54% of the residential population at the start of the test. Also, route-querying various commercial buildings revealed that there are far fewer Sims working in each building than the normal query window would have me believe.

I should explain a little bit about the numbers in the queries and graphs, as they are poorly documented and widely misunderstood.  For R and C buildings, the rightmost number is the maximum number of jobs that the building can hold.  The leftmost number is the total number that the building can use right now; it tends to be close to the rightmost number.  But neither of these numbers tells you anything about the number of Sims actually working in the building.  For that, you have to use the route query tool.

For residences, the rightmost number is the maximum number of Sims that the residence will hold, while the leftmost number is its current population.  However, neither of these numbers tells you the number of workers living in the building; again, you have to use the route query tool to determine that.  Typically, though, it's about half the population, although this proportion varies depending on the average age of the Sims.

The graphs all show the leftmost number that you see in the queries.  So they show total population for the residences, but they show only current job capacity for the jobs.  However, since your job capacity is 54% of your population, you're probably OK here, especially since a lot of that job capacity is unused.  If only a small amount of the job capacity were unused, you could be in trouble, since the wealth level of the available jobs (which is not the same as the wealth level of the building) might not match up with the wealth level of your residential Sims.

I'm glad you're getting CAM; it may very well help this problem, although that's not guaranteed.  I think that the fact that adding the outer subway belt helped somewhat indicates that you may have to add a number of more subway lines to eliminate this problem.  The fact that you have a number of subway lines displaying yellow and orange says that your current system is overloaded, even though those lines aren't going through your abandoned area.  When you're having problems, it's good to try to keep the colors no higher than green (100%), at least on most of the lines.

Also, previously I had speculated that other forms of rapid transit might suffice instead of subways.  I later realized that this is not the case.  I have an extensive tram system in the city that had abandonment problems, and the Sims could easily have taken trams all the way to their jobs.  (Trams travel at the same speed as subways, because they're really el trains in disguise.)  But the Sims didn't take them, although the tram system was otherwise well utilized.  The traffic simulator wants to see subways, at least in highly populated cities where the Sims have to travel long distances.

What about if there's no mass transit in a city at all?  Would the traffic simulator let you get away with just cars for a big city, traveling long distances?  I don't know; I'd be interested in hearing if someone has been able to do that without abandonment problems.

z

#432
Release of Simulator Z v2.1
Perfect Pathfinding Revised

This new release of Simulator Z contains a much more accurate perfect pathfinding value for the pathfinding heuristic.  Most of this post is somewhat technical; if you just want to see what this means for users and possibly download the new version of Simulator Z, skip down to the part just below the horizontal line.  Watch out for elephants along the way, though...

I was thinking more about woodb3kmaster's situation, and while I believe that what I said to him was correct, I was disappointed that the traffic simulator couldn't be tuned better to address his problem.  Yet before posting my possible solutions, I had tried tuning all the parameters in the traffic simulator that I could think of, with no effect.

Revisiting the problem, I started thinking more about the pathfinding heuristic (PH).  The perfect pathfinding value for the PH is defined to be the highest value of this constant where the fastest path is always found.  Lower values will still give the fastest path, but they will take longer to compute.  Higher values become less and less likely to give the fastest path, although the pathfinder will run faster.  This means that although values for the PH that are lower than the perfect value will take more time, the results should be identical to using the perfect pathfinding value.

At least that's how it works in standard A* pathfinding.  Unfortunately, SC4 uses a modified version of A*, in which due to the interactions with the destination finder, pathfinding deteriorates with values of the PH that are lower than the "perfect" value.  Furthermore, since one of the duties of the destination finder is to throttle the CPU usage of the pathfinder, even the perfect pathfinding value of the PH may not always find the perfect paths - in fact, sometimes it may not even find paths at all, even when valid ones exist.  Nevertheless, the perfect pathfinding value of the PH will always find the best paths possible, compared to other values of the PH.  I'll be going more into the details of the way SC4's variation of pathfinding works in my post on the destination finder, which is in preparation.

In any case, it's still important to know the value of the PH that results in perfect pathfinding, even if it's SC4's version of perfect pathfinding.  The main previous record we have of what this value is comes from Tropod, who used the value of .003 consistently; it still appears today in Simulator E.  We know that the7trumpets was the first person to come up with a perfect pathfinding version of the traffic simulator, but I have been unable to find what value he used for the PH.  In the lack of evidence to the contrary, I have been assuming that it is the same .003 that Tropod used.

When I first built Simulator Z, I wanted it to use perfect pathfinding from the start.  I figured that Tropod's value was probably correct, but I thought it was important to do a fair amount of testing to verify it.  Unfortunately, I did not understand the workings of the traffic simulator as well as I do today, and so my tests were less precise.  To be completely sure that one had found the perfect PH, one would have to check every path in the city and verify that it was the fastest path possible.  Even to do this for a single path is a lot of work, and must be done manually; to do it for the thousands of paths that exist in a large city would be impossibly time consuming.  However, values of the PH that are significantly higher than the perfect value produce many paths that are less than optimal, and this is easy to see in the traffic volume view.  Furthermore, in SC4, such values can produce abandonment, as we have seen in earlier tests in this thread.  And in general, the health of a city improves as the PH approaches its perfect value.

Using this understanding and doing a number of tests, I was able to determine that the perfect PH lay somewhere between .003 and .006.  Below .003, there were definitely no improvements to the paths, and CPU time started rising rapidly.  There also seemed to be some other subtle signs that .003 was the correct value, but they were somewhat ambiguous, and I ended up settling on .003 because it was both consistent with my tests and it was the number that Tropod claimed was the perfect value.  Recently, I have also done other experiments showing that values below .003 gain nothing.

In considering woodb3kmaster's situation, I decided to re-examine the area between .003 and .006.  This time, I had much more precise tools available.  Specifically, there's the following relationship, which I outlined a while ago:

Pathfinding Heuristic => Commute time => Desirability

To spell it out, the better the PH, the shorter the commute time, which results in higher desirability for residences.  This has shown up again and again in the tests that I have displayed here, with graphs showing the residential population migrating to higher wealth levels as the PH approached its optimum, and migrating to lower levels as the PH moved away from its optimum.  If desirability becomes too low, this results in outright abandonment of residences.

Armed with this information, I began examining the values between .003 and .006, essentially using a binary search.  When I got down to the final values, I repeated some tests to make sure I had exactly the right values.  As I narrowed in on the final value, the change in the population lines between values in the Pop & Jobs graph became unnoticeable.  At this point, I switched over to looking at the abandonment itself, which would still change significantly from one value to another.  Finally, I got a value that consistently produced the lowest abandonment over time, test after test.  I was also aware of when I had told Lenny that I was sure that the .003 value was correct to within a few percent; my tests until then didn't really provide enough data to state that with such confidence, and I was largely relying on Tropod's figure.  This time, I relied on my tests alone, tests that were much more accurate and that gave a precise answer.  And the number that they finally gave was...

&dance &dance &dance  .005797  &dance &dance &dance

What's especially interesting about this number (aside from the fact that it's surrounded by dancing elephants) is that instead of one significant digit, as the .003 value has, this value has four significant digits.  The binary search method allowed me to get down to this level of detail quickly, and it was only at this level that adjacent values began to look at all similar.  There are two effects that are in conflict across the entire range of PH values:  the better pathfinding that comes with a lower PH, and the worsening of the pathfinding that results from the destination finder's trying to limit the time that the pathfinder spends finding paths.  It would seem reasonable that these two trends would cross at the perfect PH, since lower values don't provide better pathfinding but do take more time.  And in fact, the pattern of abandonment changes right at the number I have cited.

Is this truly the perfect PH in the terms that A* defines it, or is this simply the best PH for SC4?  For the reasons I just mentioned, I believe that it is both.  However, there's not enough data to prove the first part conclusively.  Nevertheless, the second part definitely seems to be true, for reasons that I describe below, and that's enough to make this value "perfect" for SC4.

This value for the PH was sufficient to get rid of most, although not all, of the abandonment in my large city without subways, which seems to be having a problem similar to woodb3kmaster's.  I went from a state of having a large neighborhood filled with abandoned buildings to a steady state where only two or three buildings were abandoned at a time.  Many of the other buildings in the neighborhood were upgraded to their original wealth levels.  I then tried out this value for the PH on all the rest of my cities.  One city had no change, but the others had positive changes ranging from small to moderate.  I also tried this out on sumwonyuno's main city, which is now a standard part of my test suite.  Recently, I had done one test that was able to recreate his original problem.  I bulldozed a large section of the low-density commercial buildings in the outlying areas of his capital city.  Although the buildings came back fairly quickly, the number of workers did not return to its previous level.  With the new PH, however, not only did the workers return, but a widespread building spree occurred in these areas, replacing smaller buildings with slightly larger ones; their size was limited by the low-density zoning.

How accurate is this number?  Once I got down to this area, I tried out all values from .005793 to .005802, varying the tests by .000001 and repeating many of them.  So this would imply a margin of error of no more than 0.017%.  My tests of alternate numbers were not as extensive in other cities; since they did not suffer from abandonment, such a level of accuracy was not possible.  But the tests that I did do and mentioned in the previous paragraph all supported this number as being the true perfect PH for SC4.




To summarize, using the new perfect PH value of .005797 has the following effects:


  • Abandonment due to commute time, when due to limitations in the traffic simulator, is eliminated in all but the most difficult cases.  Even in those cases, it almost all disappears.
  • The desirability of all residences tends to increase; the exact amount of the increase depends on the city involved.
  • Subway usage tends to increase, and in many cases, other mass transit usage as well.  This is something that has been noted many times before when improving the PH, and is another sign that this value for the PH produces better pathfinding than what was previously considered perfect.
  • The game as a whole will run somewhat faster; this a direct result of using a higher PH.  The bigger the city, the bigger the speed increase.

I've attached a copy of Simulator Z v2.1 at the end of this post.  Zack, please give this a try and let us know how this works for you.  And sumwonyuno, please give this a try on your downtown city - I think you'll like the results.  Feedback from everyone else is welcome of course as well.

k808j

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sumwonyuno

Thanks for the "birthday present"  ;)

I tried 2.1 in Downtown Capitalis, and I'm pleased with the results.  The simulation is running a bit faster, delaying just about 1 second between months instead of 2-3 seconds.  The westbound commuters are actually getting off the freeway and driving to jobs in Downtown and Kaka'ako.

Now there's Sector 24... You may want to try some tests in this city tile.  It has a similar situation as with Sector 23.


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Shadow Assassin

Hmm, interesting.


I think I'll give this a try. Hopefully it fixes my problems with unnecessarily long routes being taken.
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z

#436
Quote from: sumwonyuno on December 23, 2009, 09:27:56 PM
Thanks for the "birthday present"  ;)
You're welcome!  And happy birthday again!   :party:

Quote from: Shadow Assassin on December 23, 2009, 10:27:17 PM
I think I'll give this a try. Hopefully it fixes my problems with unnecessarily long routes being taken.

The "speeding premium" (which is necessary for compatibility with RHW) will often cause routes to be taken that are somewhat longer than expected.  If a Sim can find a road near a road which is the shortest route, but the second road has less traffic (even if neither road is congested), then depending on the length of the Sim's trip, the distance between the roads, and the difference in traffic volume on the roads, it may be faster for the Sim to take the longer route.

tamorr

   It is good to hear that you finally have found a more reliable number to use. Great for my cities in the way I play. I can't really do any tests, but from the description analysis I believe it makes it even better for me. :) One question though...

   Are you going to make BTM Variations to this current set, or is that not needed?
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z

Quote from: tamorr on December 25, 2009, 11:11:18 AM
Are you going to make BTM Variations to this current set, or is that not needed?

The BTM variations are no longer needed in Simulator Z; in fact, they would make gameplay worse.  :o   One of the things I've discovered along the way is that there is an optimal spread of speeds for the game, and keeping to that speed range benefits the whole game.

The monorail speeds in the game are actually way out of line with real monorail speeds; for example, in Seattle, the average monorail speed (including stops) is 27 mph (43 kph).  The game's monorail speeds are much more in line with high speed rail, and the bullet train is of course a form of high speed rail.  The ratio of monorail speed to subway speed is almost exactly 2:1 since my reduction in rail speeds in Simulator Z; in the original BTM simulator, the ratio was exactly 2:1, because subway speeds were much higher.  So bullet trains still retain a substantial speed advantage over all other forms of travel, while not disrupting the rest of the game.

k808j


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