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NAM Traffic Simulator Development and Theory

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

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z

These are excellent questions, and I'm happy to have the opportunity to address them here.  I'll first discuss the Transit Switch Entry Costs, since this issue is a bit simpler, and my basic proposal has been incorporated into the PIM-X tool.

Setting the Transit Switch Entry Cost to the proper value is very important.  If it is set too low, then pedestrians and possibly other travel types may cut across the lot, leading to what is commonly known as "shortcutting"; the travel time of the station's main travel type(s) is also distorted.  If the Transit Switch Entry Cost is set too high, the result can be even worse, as after a certain point Sims may not use the station at all, and in some cases the entire transit line may become abandoned.  The cause of these problems may be very difficult to detect, and for the average user, it may appear that the traffic simulator or some other aspect of the game is malfunctioning.

The game is designed so that it works best when the Transit Switch Entry Cost (TSEC) for a particular travel type allows that travel type to move through a transit-enabled (TE) lot at the same speed that the travel type would travel at on the adjoining network.  Based on this, and using the speeds for travel types found in the NAM Unified Traffic Simulator, the proper TSECs for various transit stations are as follows:

Pedestrians, bus, and subway stations: .064
Street stations (e.g., RTMT): .035
Road and avenue stations: .02
One-way Road Stations: .013
Highway stations: .0064
El rail, GLR, and freight rail stations: .0091
Passenger rail stations: .0069
Monorail and HSR stations: .0043

Bus stops and subway stations have the same TSEC as pedestrians because buses don't actually drive through bus stops, and subway trains are not affected by the TSEC.  However, pedestrians walk through both types of stations, so the TSEC is set for them.

The above values are incorporated into the current version of the PIM-X tool (SC4 PIM), specifically in the current version of the SC4PIM New Properties XML Update.  However, transit stations that service multiple travel types in addition to pedestrians must have their TSEC set manually.  For such stations, the following rule should be used; this rule covers all situations:

The formula for the transit switch entry cost for any station is .96/speed, where "speed" is the speed of the fastest travel type that is designed to pass completely through the station at normal speed (excluding subways).  If the travel type passes next to the station instead of going through it or if there is no through travel type (such as in parking lots), the pedestrian speed should be used in that formula.




Now on to capacities.  First I'll give the rationale, and then the various capacities and formulae.  If you just want to see the latter, you can just skip to the end of the post.

The way the game is presented to us, transit stations appear to act much like networks.  They have fixed capacities, and when these capacities are exceeded, transit stations appear to suffer their own form of congestion - their "service quality" declines.  Transit stations are even shown in the Traffic Congestion Data View.  When their usage is no more than 100%, they're is shown as green, just like networks, but as their usage passes 100% and their service quality declines, their color goes from green to yellow to orange to red - again, just like networks.  We are led to believe that a transit stations at 300% capacity, which shows up as bright red in the congestion data view, is performing quite poorly compared to one operating at, say, 30% of capacity.

This is all completely false, and Maxis knew it.  A station running at 300% of capacity has the same "service quality" as a station running at 30% of capacity; they operate identically.  Maxis actually could have implemented such a service quality approach fairly easily, by multiplying the Transit Switch Entry Cost by the inverse of the Congestion vs Speed curve.  But as we know, they didn't, and in fact the TSEC is used by Maxis only for toll booths.

If this were the whole story, nothing would need to be done here; the current capacities could be used for transit stations, and though their "service quality" would be displayed inaccurately, no harm would be done.  But it's been know for a number of years by some players that there's a maximum number of Sims that a transit station will process in a day.  However, the numbers reported for this limited varied, although they were always a certain multiple of the station's capacity.  Two years ago, I set out to verify that such a number existed, and if it did, to find out what it was; RippleJet later joined me in these experiments, and Tarkus participated in the thread where the results were presented in depth.

Although I verified that the limit existed, I did so mostly in trivial cases.  RippleJet's experiments were the first to use realistic station capacities.  His results can be found in this post.  Some of my experiments showed slightly different aspects of the problem; one of the more interesting ones can be found in this post.

Between these experiments and others that preceded and followed them, the following facts were determined:  All stations have a fixed capacity that is some multiple of their nominal capacity.  Until this fixed capacity is reached, they suffer no performance degradation; they are completely unaffected by high usage, even when it's well over 100%.  Once the fixed capacity is reached, however, the stations simply stop working for the day.  No more Sims are permitted through the stations via any network.  The stations are effectively broken for the rest of the day.

What is this fixed capacity?  Different experiments have yielded different numbers, as have different in-game situations.  The maximum capacity found by RippleJet's experiments was 400% of the nominal capacity, and although this number has been seen in various other situations since then, no lower maximum has been reported.  Somewhat higher maximums have been reported for specific stations, but no pattern has been observed.  Occasionally people report much higher maximums, but for standard stations, this seems to be due to the fact that the traffic simulator will let as many Sims who want to use the station use it the first time, and only in subsequent runs will it scale back the station usage.  This is in keeping with other known behaviors of the traffic simulator.

If a station breaks at 400% of its nominal capacity, we clearly don't want that to happen; that doesn't correspond to any RL event, and is essentially just a bug.  Therefore, we need to set station capacities high enough so that their usage never exceeds 400% of their nominal capacity.  How high is that?  In other words, what's the maximum amount of traffic that can be expected through a station?

Below is an example of a station in an ordinary city; this city was not designed to test station capacities, but merely provides a good example:


The station is mostly hidden by the query; it is a combination bus and tram station for tram-in-road, and you can see a bit of the tram shelter sticking out just past the number 980.  You'll also notice that for RTMT stations, "Service quality" has been renamed "Reserve Capacity," since a reduction in this graphic does not imply a reduction of service quality at the station, even in circumstances such as these.

One of the things that's interesting here is that this is no megalopolis; the population here is only around 150,000.  When you figure that about half of that is the city's workforce, and the query includes both commute periods, you see that almost the entire workforce of this city is going through this station.  Looking closely at the picture, it's easy to see why; this station gives access to the rail station, which is the main (and fastest) connection between residences and jobs.

If we were to do a straight extrapolation here, we would come to the conclusion that in order to support cities containing millions of Sims, seven-figure station capacities would be necessary.  But situations such as this don't arise in such cities (fortunately), as their increased density tends to greatly increase the number of ways for Sims to get from their homes to their jobs.  In reality, the station above is the most heavily used station I have ever seen.  I think that we would be safe in saying that no station would need a capacity of more than 200,000; if one did, there would be larger variants available, or multiple stations could be used.

Now we're ready to look at which capacities we should actually use.  There are three basic approaches here.  For the first one, if 200,000 is really a safe capacity for virtually all stations, and the true capacity is at least 400% of the nominal capacity, then we could simply use the following rule for nominal capacities:

All Stations:  50,000

From the point of view of game play, this would work out a lot better than the current capacity system.  Currently, PIM-X gives single-tile bus stations a capacity of 1000 and single-tile subway stations a capacity of 2000, yet it is not at all unusual to see five-figure usage numbers for this type of station.  This means that stations with capacities set this low, or even in this range, are going to break frequently.  Players may not notice the details of this type of breakage, but they do notice the red in their congestion maps, and undoubtedly the single biggest complaint players have about transit stations is that their capacities are too low.  When a subway line has a capacity of 30,000 (as in the High version of the NAM traffic simulator), and players have erected blocks of buildings where each building houses thousands of Sims, then a subway station every few blocks (which is much more frequent than in real cities) with a capacity of a few thousand just isn't going to cut it; a single tall residence could saturate such a station.  The Maxis transit stations simply were not built with today's custom content in mind, and they and other stations with similar capacities simply do not function well at all in that environment.

On the other hand, a single capacity for every type of transit station simply doesn't look good.  Eye candy is not a bad thing; a BATter's job is to create beautiful eye candy.  So in this case, it looks a lot better if we create numerical eye candy - capacities that are sufficient for each type of station, but which don't get exceeded, so that the station doesn't break.  This also allows us to use capacities lower than 50,000 for many types of stations, because many types of stations will never approach that usage level.

The question at this point then becomes:  What capacities should we use?  In terms of game play, the capacity required for a particular type of station bears very little relationship to the size of the station.  So for this purpose, we just need to know what the minimum capacity should be for a given type of station.  When I first started looking at the issue of station capacities more than two years ago, one guideline I kept in mind was that in RL, stations rarely get congested before the networks they serve.  The reason for this is that it is much easier and cheaper to overbuild a station than to overbuild an entire network.  But what formula should be used for determining these station capacities?

There have been many formulas proposed, but I found that none of them gave satisfactory results.  I think that the reason for this is that all the formulas I saw had station capacities increase linearly with the capacities of the networks that they served, while what I was seeing was that the proper growth curve was more of a logarithmic one.  I found that the formula used in RTMT by Cogeo produced capacities that seemed to come closest to actual usage needs, although being basically a linear formula, it produced numbers that were about right on the high end for complex stations, but were too low on the low end for simple stations.  I found that by doubling the low end numbers, leaving the high end numbers the same, and adjusting the numbers in the middle accordingly, I got capacities that worked extremely well.  As Simulator Z had not been built yet, this was all done using the CAM traffic simulator, which had capacities approximately the same as the High version of the current NAM traffic simulator.  Yet these station capacities still work fine today; the only change I've made is to reduce the bus capacity somewhat, since the potential volume of buses has been limited because buses now contribute to traffic congestion, whereas they didn't in the original Maxis traffic simulator.

The question may be raised at this point as to whether the capacities used for RTMT stations, and inline stations in general, are valid for all stations, since station usage for these two classes of stations includes all through traffic.  I have found the answer to be a clear "Yes."  The reason for this answer is that SC4 traffic does not behave the same as real world traffic; much of the differences can ultimately be pinpointed to the fact that most travel distances in SC4 are much shorter than in the real world.  As a result, for example, instead of taking a train for at least several kilometers, Sims tend to travel much shorter distances.  This means that virtually the entire traffic of a train line may enter or exit at a single stop, and this may happen at multiple stations along the train line.  For such stations, there really is no difference between through traffic and traffic that enters or exits the line at that station.

For buses, the situation is slightly different, but the ratio of cars to buses varies so greatly on any given road that I have found that here too, an RTMT-type bus stop requires the same capacity as a roadside bus stop.

Based on all of this, and on extensive experience with my RTMT and traffic simulator experiments, I would recommend the following base capacities for transit stations.  Where these transit stations are supported by RTMT, these are the RTMT capacities.

Bus:                      17,000
Subway:               24,000
Freight train:        15,000
Passenger train:   30,000
El rail:                    30,000
Monorail:               45,000
Parking facility:     30,000

The astute reader will notice that all of these capacities are lower than the 50,000 mentioned earlier; the reason for this is that each of these stations handles just a single travel type, whereas the 50,000 is designed for a broader range of stations.

The type of differentiation in the above table certainly seems better than the one-size-fits-all figure of 50,000, but it still makes no differentiation between different sizes of stations, nor does it account for stations that handle multiple travel types.  While accounting for this in the stations that I use and have modified, I have been doing this on a somewhat ad hoc basis, ending up with something that seemed about right.  In order to be more systematic, I have come up with formulas  that produce numbers very close to those that I have been using; these formulas mean that PIM-X could eventually be used to produce reasonable station capacities for any type of station.  Unlike the TSEC, there is no "exact" correct capacity, so some rounding can be done by the developer.  For example, I had been using a capacity of 50,000 for the Maxis Grand Railroad Station; the formula that follows yields 51,000, but this is one of those cases where rounding off (in this case to 50,000) makes a lot of sense.

The formulas I have devised for station capacities follow.  For stations with buildings, only the first floor of the building is used in calculating the station's capacity, as additional floors are generally not used for passenger waiting space.  Another point to consider in these formulas is that the bigger the station is, the less distance the Sims have to walk to get to any part of it.  Since the whole station is fairly monolithic as far as the traffic simulator is concerned, bigger stations therefore do serve more Sims, though not by all that much.

Here are the formulas:

Bus stops and stations:  17,000 for the first tile, plus 1000 for every additional tile on the lot.  Large bus stops may not have buildings as such, which is why the tile count of the lot is used.

Subway and Other Underground Rail Stations:  24,000 for the first tile, plus 2000 for each additional tile in the lot.  This time, we're talking about the lot instead of the building due to the underground nature of these networks.

Passenger train (may include freight): 10,000 per tile for the first three tiles of track served by the station, plus 2000 for each additional tile.  For stations serving multiple tracks, additional tracks are counted at the rate of 10,000 for the first tile plus 1000 for each additional tile.  If the tracks are sidings and not through tracks, such as in the Maxis Grand Railroad Station, each tile of siding is counted at 500 per tile.  Buildings attached to train stations also add 500 per tile.

Freight train only:  5000 per tile for the first three tiles of track, plus 1000 per tile after that.  Sidings add another 500 per tile.  Nothing is added for the size of the lot; freight lots tend to contain all sorts of things, most of which just sits there forever.  Also, the size of the lot is somewhat proportional to the number of tiles of track served, so it's implicitly counted to some extent.

El rail:  Same formula as for passenger rail.

Monorail and HSR:  Works the same as passenger rail, but all capacities are 50% higher.

Parking facilities:  1000 per tile.  For multi-level garages, only the tiles containing the garage count, and their number is multiplied by the number of levels of the garage.  Underground garages have a flat capacity of 50,000, since they don't have any real dimensions.

There are also rules for combining these basic types.  For example, adding a parking facility adds the standard 1000 per tile for the parking lot; if it's a garage, the standard garage rule applies.  The one exception here is a parking lot added to a subway station, as it implies a bigger station.  In this case, it's 2000 per tile of parking lot; for a garage, it's 2000 per tile for the first level, but the standard 1000 per tile for additional levels.  Adding an underground garage to a station adds 15,000 to its capacity.

If the station serves multiple networks, the basic rules are used for the highest capacity network.  After that, for additional rail types, 9000 is added for the first tile of a rail line, and 500 is added for each additional tile.  (For subways, the length of the subway line beneath the station is counted.)  For buses, 4000 is added for the first tile of the rail line, and 500 is added for each additional rail tile.  Sidings and buildings are not counted here; they've been counted once, and that's enough.

That should cover it.  Although the station capacities produced by these rules are large, they are just large enough to assure that stations won't break under any but the most extreme usage.  They also produce station capacities that rise nicely with station size and layout.  Finally, they happen to produce capacities very close to the ones I've been using all along, and which work very well in a wide variety of situations.




The part of this post between the two horizontal lines is a proposal I made at the BSC two months ago.  So far, there have been no responses.  :(   I can understand this, though; the post is quite long and somewhat complex, and people have the rest of SC4 and RL to deal with.  So I am waiting patiently for a response. :)  In the mean time, I would certainly recommend these numbers and formulae to anyone building transit stations, or who want to make their existing transit stations work better.  It is completely safe to change these numbers for your existing transit stations; however, the new numbers will affect only newly plopped stations.  As for the tool to use to make such changes, I find Ilive's Reader to work quite well, especially since it has various methods for copying and pasting.  If you are going to change the Maxis stops, you should use the Patch facility of the Reader to create a new file rather than edit SimCity_1.dat directly.  Or you can wait a little while, and I will release a complete set of updated Maxis transit stations and ports.

In order to avoid poorly functioning stations, I have also suggested that rules for TSECs and capacities be applied to existing stations on the LEX.  I would estimate that it would take one person just a few hours to convert all the stations properly.  Again, I have made this proposal at the BSC, but so far there has been no response.  BSC members are some of the busiest and most productive people at SC4, though, so I understand that it may take them a while to get to this.  However, if other people would like to see better functioning transit stations, chances are that this could happen sooner rather than later.  So if readers of this post would like to see the capacity standard incorporated into PIM-X, and both the TSEC and capacity standards applied to all LEX transit stations, including current ones, please post here.  I'm sure that our dedicated  BSC group would take notice of any significant demand for the application of such standards. :)

H2Odk

Thanks for the quick response :)

So if I where to make a "patch"/override for the Maxis stations (I know this really isn't the place to ask this) with iLive Reader (1.4), I should:

  • "Group Add to Patch" all the stations/bus stops. (could I just add the "0x02" exemplar?)
  • When all is added, "Create DAT" named eg. "zMaxisOverrides.dat"
  • Open this DAT, and make the Edits there.

With your formula this is what I get:
Bus:               TSEC 0.064, TSTC 17000 (1*17000)
Subway:            TSEC 0.064, TSTC 24000 (1*24000)
Freight train:     TSEC 0.0091, TSTC 15000 (3*5000)
Passenger train:   TSEC 0.064 (speed inside the building is "Walk"), TSTC 20000 (2*10000) (could be 30000 since it is a 2x3 lot)
El rail:           TSEC 0.0091, TSTC 30000 (3*10000)
Monorail:          TSEC 0.0043, TSTC 45000 (3*10000*1.5)
Parking Garage:    TSEC 0.064 (speed inside the building is "Walk"), TSTC 30000 (2*3*5*1000)
Subway to El-Rail: TSEC 0.0091, TSTC ?? (should probably just be set to very high number)


I do not fully understand the Grand Station. I do understand (I hope) that it is the building that is the TS and not the lot, so the TSEC should probably be set to walking speed, since that is the only speed inside the building. But I am not sure on how many tracks it serve, and how this should be counted. I do understand that it is Transit Enabled for one track, I also understand that I can just use my best judgment here, but I would like to know how you see it.

I really want to get the traffic right from the start, since (IMO) this is the most important part of SC4. I am also sorry cluttering this thread with some noob modding questions  :-[

z

Quote from: H2Odk on November 13, 2010, 06:55:18 AM
So if I where to make a "patch"/override for the Maxis stations (I know this really isn't the place to ask this) with iLive Reader (1.4), I should:

  • "Group Add to Patch" all the stations/bus stops. (could I just add the "0x02" exemplar?)
  • When all is added, "Create DAT" named eg. "zMaxisOverrides.dat"
  • Open this DAT, and make the Edits there.

Yes, this is correct.  You don't need the 'z' in front of the file name, though, as all files in your Plugins folder automatically override anything in SimCity_1.dat.  (There are some obscure exceptions to this rule, but they don't apply here.)  The new file can be put anywhere you want in your Plugins folders.

Quote
With your formula this is what I get:
Bus:               TSEC 0.064, TSTC 17000 (1*17000)
Subway:            TSEC 0.064, TSTC 24000 (1*24000)
Freight train:     TSEC 0.0091, TSTC 15000 (3*5000)
Passenger train:   TSEC 0.064 (speed inside the building is "Walk"), TSTC 20000 (2*10000) (could be 30000 since it is a 2x3 lot)
El rail:           TSEC 0.0091, TSTC 30000 (3*10000)
Monorail:          TSEC 0.0043, TSTC 45000 (3*10000*1.5)
Parking Garage:    TSEC 0.064 (speed inside the building is "Walk"), TSTC 30000 (2*3*5*1000)
Subway to El-Rail: TSEC 0.0091, TSTC ?? (should probably just be set to very high number)


This is all correct except for the capacity for the passenger train station, which according to the formula should be 23,000.  As for the Subway to El-Rail transition, this is functionally an extension of the network, so the main concern here is that it shouldn't be a bottleneck.  For this reason, I use the network capacity of the Ultra version of the traffic simulator, which is 62,500.

Quote
I do not fully understand the Grand Station. I do understand (I hope) that it is the building that is the TS and not the lot, so the TSEC should probably be set to walking speed, since that is the only speed inside the building. But I am not sure on how many tracks it serve, and how this should be counted. I do understand that it is Transit Enabled for one track, I also understand that I can just use my best judgment here, but I would like to know how you see it.

The Grand Station has the tracks running through it, so you need to use the rail TSEC of .0069.  If you follow the somewhat complex formula required for this station's capacity, you get 51,000.  Since this is what I have called an "eye candy" number, I have simply rounded it down to 50,000, which is numerically prettier eye candy. :)

QuoteI am also sorry cluttering this thread with some noob modding questions  :-[

No problem!  $%Grinno$%   I think that many people will find it useful to have these numbers and formulae posted in a single place, and this thread seems to be the most logical place for them.  As your most recent post is a direct follow-up, it makes sense to put it here also.  Other than that, for general support questions the NAM Unified Traffic Simulator and Data View Help thread can be used.

H2Odk

Quote from: z on November 13, 2010, 11:15:39 AM
The Grand Station has the tracks running through it, so you need to use the rail TSEC of .0069.  If you follow the somewhat complex formula required for this station's capacity, you get 51,000.  Since this is what I have called an "eye candy" number, I have simply rounded it down to 50,000, which is numerically prettier eye candy. :)
ok.. So despite the only speed inside the Exemplar that has the TSEC is walking speed, I have to use the max speed of what is moving in the LOT. When I looked at it in the Reader I got the impression that they where different things

z

Quote from: H2Odk on November 13, 2010, 01:00:15 PM
ok.. So despite the only speed inside the Exemplar that has the TSEC is walking speed...

I'm not sure what you're referring to here.  Could you please explain?

QuoteI have to use the max speed of what is moving in the LOT.

Yes, that is correct.

H2Odk

Quote from: z on November 13, 2010, 03:10:17 PM
I'm not sure what you're referring to here.  Could you please explain?

This is the TSEC for the Grand Station:

Transit Switch Point   0xE90E25A1   Uint8   20   Outside-to-Inside,All Sides,Walk,Walk,Outside-to-Inside,All Sides,Drive Car,Walk,Outside-to-Inside,All Sides,Ride Train,Walk,Inside-to-Outside,All Sides,Walk,Ride Train,Inside-to-Outside,All Sides,Walk,Walk

The only "speed" inside is "Walk". I thought this was what mattered because eg. the El-Rail Station has "Ride El Train" inside.

Transit Switch Point   0xE90E25A1   Uint8   16   Outside-to-Inside,West+East,Ride El Train,Ride El Train,Inside-to-Outside,West+East,Ride El Train,Ride El Train,Outside-to-Inside,All Sides,Walk,Ride El Train,Inside-to-Outside,All Sides,Ride El Train,Walk

z

Quote from: H2Odk on November 13, 2010, 04:03:51 PM
This is the TSEC for the Grand Station:

...Outside-to-Inside,All Sides,Ride Train,Walk,Inside-to-Outside,All Sides,Walk,Ride Train...

This is the way the trains get across the station.  All travel types travel at the same speed in a TE lot, so it doesn't matter if they alternate between train and pedestrians as they do here.  The automata appear as continuous trains, since trains are on the outside of every square.

The El Rail station method is just an alternate way of doing things.

You can't just go by the transit switch point; you have to look at the lot itself to see what's happening.  For the best view of this, I find SC4Tool to be the most useful.  But generally, you can tell just by plopping the lot whether or not travel types pass through it.

pepsibottle1

Very informative article, and I have to take the time to applaud you for everything you have done to contribute to the commuting redundancies.

Even though I'm only 16, I do take a great liking into the way that traffic flows and works. Don't ask me why, but I'm a nut when it comes to highways, roads, commuting trends and traffic fundamentals. Maybe it's because I live in Norfolk, VA and I've been exposed to such a vast transit network. With that said, I've downloaded the ilive reader and am willing to step up to the plate and experiment with the simulator. I have a lot of free time so I'll be able to really help you guys out with this. If you have any questions about anything, ask me and I'll be more than willing to share my philosophy on traffic fundamentals. I'm not a pro or a traffic engineer, but living in the Hampton Roads region, I've learned quite a bit about where people choose to work and how they decide to get there. You have to bear with me, I don't use the tram or ground rail stuff though, using that ingame is way too confusing. I stick to roadways pretty much. If you know anything about the region, you know about the Hampton Roads Bridge Tunnel. Mass chaos! Well, I-64, I-264 and I-464 is basically mass chaos on a 24/7 sehedule. In other words, Hampton Roads in the mecca of gridlock.

I'll share my results with you if I come across anything interesting. For now though, thanks for all that you guys have done!
I love Simcity 4!

stmnf2

#528
Hi
I haven't read the entire topic, so I'm sorry if this has been discussed already.
I'm about the bus traffic in NAM. Why it makes the same load on the road and the same jams as car traffic? I think it's not quite correct.
But zero load, as in the original SC4, also isn't very good. I think the best ratio is about 0.2 of car traffic.
Is any way to modify it?
Thanks in advance, sorry for my English.

z

There is no way to modify the load factor of the various vehicles, largely because vehicles don't actually exist, aside from the automata.  There are simply Sims that follow the rules of buses, cars, or whatever.  The current situation with regard to buses is not ideal, but it's the best we can do; it works far better for the traffic simulation than the only other alternative, which is the zero load factor of the original SC4.  Maxis was forced to make that choice because the original traffic simulator was not tuned well enough to permit buses to be counted as part of traffic.

stmnf2

Well, it is clear.
It turns out I'm, as mayor, not very interested in developing land transport because it does not improve the situation on the roads. &mmm

z

There are other advantages to buses that you may be overlooking, though.  For example, if you have subways or various other rail lines without parking facilities nearby, buses are the ideal way to transport Sims to them.  All the various types of rail transport are faster than standard roads, and this way, traffic is removed from the roads.  ;)

z

Although the current NAM traffic simulator treats buses in a more realistic way than previous traffic simulators, due to limitations in the traffic simulator, this treatment is not perfect, and some people prefer to have buses behave the way they did in previous traffic simulators, including the original Maxis traffic simulator.  As a result, I have asked Stefan to add this option to the Traffic Simulator Configuration Tool, and it is now present near the top of the tool as Buses contribute to traffic.  Full documentation for this option has been included in the revised User Guide, and I have also included a copy below.  This version of the Traffic Simulator Configuration Tool will be available in the next release of the NAM, but you can also get it now in the newly upgraded NAM Traffic Subsystem.




Buses contribute to traffic

In the original Maxis traffic simulator, buses did not contribute to traffic congestion; the pathfinder was not tuned tightly enough to make this workable even if it had been desired.  Experiments showed that turning this field on in the original simulator would have simply increased the existing traffic congestion without having any significant benefit.

However, in the NAM traffic simulator, the pathfinder has been tuned so that it is much more intelligent than in the original Maxis traffic simulator, and it is now possible to allow buses to contribute to traffic (just like every other vehicle travel type) without creating any problems.  In fact, the traffic simulation as a whole runs much better this way.  The reason for this is that in the original Maxis traffic simulator, buses became the travel type of last resort; if congestion on the roads or most rails became too great, the traffic simulator could always cram more Sims into buses and thereby reduce congestion arbitrarily, since all the road networks had an infinite capacity for buses. This was highly unrealistic, and had the Sims at times abandoning faster forms of transport for buses simply to avoid congestion.

The current NAM traffic simulator avoids this problem by letting buses contribute to traffic.  However, buses, like all vehicles in SC4, are really single-passenger vehicles, and so some of their usefulness is lost in that they are now no more efficient than cars at transporting Sims.  However, they are still very useful for those Sims who prefer to use mass transit, and even more importantly, they are extremely efficient at ferrying Sims to high speed rapid transit (i.e., the various rail networks) where no parking exists.  So although each setting of this property has certain drawbacks, the traffic simulator works better and provides a more accurate traffic simulation when this field is checked, which is its original state..

However, some people like the way the original Maxis traffic simulator worked, or they just like to have increased use of buses.  For these people, this field can be unchecked, and the behavior of the original Maxis traffic simulator will be restored with regard to buses. If this is done, though, the traffic simulation as a whole becomes slightly degraded as a result.  The amount of degradation is fairly minimal, though, so as long as it is understood that this happens, unchecking this field should not cause any major problems.

stmnf2

I think that zero bus contribution to traffic is closer to reality than 100% one.
In fact, 1 bus carries 30-50 people and takes place on the road as about 3 cars. So the real contribution is a maximum of 10-20%.
In order to avoid an excessive increase in the use of buses by the simulator, we can slightly decrease their speed and set Transit Switch Entry Cost for bus stops.

z

Quote from: stmnf2 on May 19, 2011, 11:19:40 AM
I think that zero bus contribution to traffic is closer to reality than 100% one.
In fact, 1 bus carries 30-50 people and takes place on the road as about 3 cars.

This is true, but it doesn't take into account the way the traffic simulator will shift almost all other forms of mass transit into buses when traffic gets congested, assuming that buses have zero contribution to traffic.

QuoteSo the real contribution is a maximum of 10-20%.

In the real world, it's significantly more than that, especially on two-lane roads.  Buses have to stop every few blocks, which slows down the whole stream of traffic behind them.  This is much more than the effect of three cars.

QuoteIn order to avoid an excessive increase in the use of buses by the simulator, we can slightly decrease their speed and set Transit Switch Entry Cost for bus stops.

Setting the Transit Switch Entry Cost properly is always a good idea.  But you don't want to set it higher than the standard formula, nor do you want to decrease bus speeds.  If you do either of these, you will find that bus usage in uncongested areas becomes less than under the default settings of the NAM traffic simulator.

z

A bug was recently discovered in the Traffic Simulator Configuration Tool whereby the capacities for one-way roads were being set too low.  This bug has now been fixed, and the fixed version is on the LEX.  Anyone who has downloaded a previous version of the TSCT should replace it with this version.  If you have used a previous version of the TSCT, then after downloading the new version, run it, make sure that the Base Network Capacity setting and Network Capacity Multiplier are what you want, and then save the new configuration.  This will ensure that all network capacities are set properly.

Original

Hey everyone,

I have a bit of a problem here, I am trying to get my automata to appear more. I've tried all the simulators, and yes they do work. The only thing though is that the morning commute is the only one that is shown through 24 hrs. So it looks like all my sims are travelling to downtown through day and night and none of them ever return home. This is highly unrealistic :(

Is there anyway to get the morning and evening commute to possibly show up at the same time for 24 hrs?

, Kohtem

z

This is actually not controlled by the traffic simulator; it's an issue with the automata controller.  I'd suggest that you post your question in the thread entitled NAM Issues Thread - PLEASE POST YOUR NAM QUESTIONS AND PROBLEMS HERE.

Also, this thread is for further development of the traffic simulator.  For questions concerning its usage, please use the NAM Unified Traffic Simulator and Data View Help thread.

b22rian

Steve ,

         I know this is a long ways off because we are both fully committed to
getting RTMt released. But once that has been completed, do you have any
thoughts about getting back into a little traffic Sim research ?
      The way I recall it, there was still much research we can do with the
Destination finder side of the traffic Simulator , I really miss the old days of
traffic research with you, me, lDog, and there were others along the way who
were very helpful. I know you would also like to continue on with ESURE-2, but
I was just curious if you ever feel the cravings to go back to traffic research at
all ?

Your good friend, Brian  ;)

z

At this point, there's really not much to be done with the SC4 traffic simulator.  It's fairly well understood, the parts that can be tuned have been tuned reasonably well, and the parts that are problematic are in the executable, and therefore beyond our reach.

I think that at this point, the destination finder is among the parts that are fairly well understood.  RippleJet even did some experiments a few years ago showing in a fair amount of detail how it went about picking its destinations.  Much of the rest of its operation was inferred by observing its behavior.  It's the destination finder that has the most problems of any part of the traffic simulator, but unfortunately we are not able to access it and thereby address them.  So I don't expect any more major activity on the traffic simulator front.  It's possible that someone might find a few parameters that can be tuned a little better, but I think that the reason that this hasn't happened recently is that we've hit the point of diminishing returns.

All that being said, there is a little tune-up that I've been considering for a while.  I've recently run some tests that confirmed it would be helpful, so I'll run it by the rest of the NAM Team, and if they agree, it should make its way into the traffic simulator pretty soon.