The NAM Unified Traffic Simulator (or the NAM Simulator, for short) is a traffic simulator that is derived from the original Maxis traffic simulator, but is also built upon the knowledge gained from all previous NAM traffic simulators, including work by the7trumpets, Tropod, jplumbley, mott, and z. It uses the Simulator Z core; what makes it a unified simulator is that it makes available to the player all the main features found in all previous traffic simulators. What makes this possible is the Traffic Simulator Configuration Tool (TSCT), which can be used to customize the NAM Simulator in any of these ways, and it also allows the ordinary player to safely customize the traffic simulator in ways that were not possible previously.  The TSCT is available as an option in the NAM installer when the option "I want to build a custom simulator" is chosen from the options page of the NAM installer.

Since the NAM Simulator evolved from Simulator Z, many of the features listed here for the NAM Simulator were also present in various versions of Simulator Z. However, many of these versions were never released together with the NAM, and so most people will be seeing the features they contained for the first time here.

One of the main areas of the work on the NAM Simulator involved increasing the efficiency of the pathfinder to close to its theoretical maximum. One of the main ways this was accomplished was by using a much more accurate version of the "perfect pathfinding" heuristic than had been available in previous traffic simulators. Also, the Sims' maximum commute time was increased to be closer to real-world conditions. These changes allow a smoother distribution of traffic throughout the city, with typically less congestion. At the same time, the congestion that does exist no longer leads to abandonment due to commute time; Sims know that they occasionally have to sit through traffic jams, and are a bit more patient. Better pathfinding also means that Sims act much smarter about finding jobs and routes to them; this also results in less abandonment due to commute time. As in the real world, zones can be farther apart without causing problems; this is especially helpful when building existing cities to scale. Finally, running the pathfinder with near-optimum settings allows the simulator to run up to several times as fast as previous traffic simulators.

The second major area of work on the NAM Simulator involved a more flexible distribution of traffic among the various travel types. In combination with the pathfinder upgrading, this allows buses to be counted toward traffic and congestion, just like all other vehicles. This is a significant change from all previous simulators, and it's an important point to remember when planning your transportation infrastructure. More flexible distribution of traffic also means that the NAM Simulator is much more dynamic about allowing Sims to choose their transportation. In cities with excellent highways and road capacity, car usage has been measured at over six times that of previous simulators. Yet for cities with less extensive road networks and reasonable mass transit, car usage is actually less than in previous traffic simulators.

For those who wish to have a deeper understanding of the principles behind the traffic simulator, A Guide to the Operation of the Traffic Simulator  is recommended. 

Other changes in the NAM Simulator from previous traffic simulators include the following:

  • More realistic subway costs. Subways in Sim City are tremendously underpriced compared to the real world. The improvements to the pathfinder have made huge networks of subways less necessary, so the monthly cost for subway tiles has been multiplied by six to add a little more realism.
  • More realistic air pollution due to traffic. Until now, the amount of air pollution emitted by traffic has been unchanged from the original game, where it was based on cities that had far less traffic capacity than that used by any of the recent traffic simulators. To keep the amount of air pollution emitted by traffic to a more realistic amount, the proportion of traffic air pollution to actual traffic has been lowered in the NAM Simulator. This lower proportion is linked to the Clean Air Act, so it is in effect only when the Clean Air Act is enabled.
  • More accurate numbers for the Commute Time Graph. Due to a bug in the game, it is impossible to get accurate Commute Time Graph numbers for all situations. However, the NAM Simulator has adjusted the scaling of this graph to provide reasonably accurate numbers for most situations.
  • Improved intersection effects. Despite the appearance of stoplights at intersections, Sims don't actually stop; they don't even slow down unless congestion is present around the intersection. The NAM Simulator provides much more congestion around heavily-traveled intersections, thereby doing a better job of simulating stop lights and stop signs.
  • Greater Monorail and High Speed Rail (HSR) usage. Due to a bug in the game, Monorail and HSR usage is generally less than it should be, sometimes by quite a bit. The NAM Simulator compensates for this bug by raising monorail and HSR usage to appropriate levels.
  • Monorail and High Speed Rail trains have been fixed to contribute to and be affected by traffic congestion, just like all other vehicles.
  • Greater highway usage. The traffic simulator has been tuned so that Sims use highways much more than ever before. This usage still tends to fall short of real world usage, though, due to the structure of the game. The amount of rapid transit available in a city will also have a big effect on highway usage.
  • All mass transit speeds have been recalibrated to provide a more realistic simulation.
  • Improved customer levels for businesses.
  • Capacities and speeds of one-way roads have been raised to duplicate the real-world advantage of these roads.
  • Street capacities have been raised so that they reflect the capacities implied by their speed limits.

There are Park and Ride versions of the NAM Simulator; these can be enabled with the Traffic Simulator Configuration Tool (TSCT), mentioned above.  Park and Ride changes the game slightly so that cars cannot reach their destination directly. Instead, those Sims who prefer to drive must park near some sort of mass transit station, and then take mass transit to the stop closest to their workplace. From here, they must walk the rest of the way. For this to work well, you need to have an extensive mass transit system. You also need to build parking lots and/or parking garages near key mass transit stops; generally the best places are at the edges of your residential areas that are closest to your jobs. Or you could just build parking facilities near the Sims' jobs (the ones that come with buildings generally don't count), but this really defeats the main purpose of Park and Ride.

What are the different versions of the NAM Simulator, and how are they used?

The NAM Simulator comes in five capacity versions - Classic, Low, Medium, High, and Ultra. The name of the version refers to the network capacities in the simulator. The name "Classic" refers to the fact that the capacities are essentially the same as in the original Maxis traffic simulator. The following is a list of the network capacities for each version of the simulator; all capacities are per tile (for two-tile networks such as the Avenue and Highways, multiply the value by 2):

One-Way Road:180036006000900018000
Highway (Ground and Elevated):40009000150002250045000
Subway/Elevated Rail/Ground Light Rail:300010000160003000065200
Monorail/High Speed Rail:300010000160003000065200

All versions of the NAM Traffic Simulator use the same speed settings for the various networks, as shown below:

Vehicle TypeStreetRoadAvenueOne-Way RoadGround/Elevated HighwayRealHighway
Freight Truck25404560130130
Vehicle TypeRail
Passenger Train140
Freight Train105
Vehicle TypeGround/Elevated Light Rail/Subway
Light Rail Train/Tram105
Vehicle TypeMonorail/High Speed Rail
Monorail/High Speed Rail Train220

Which simulator version is appropriate for a particular city depends primarily on two things: the population of the city, and the amount of rapid transit (rails) available. Less capacity is needed for lower population cities, but less capacity is also required for cities with a lot of rapid transit. For example, a city of two million Sims has been run quite successfully using the Low capacity version of the NAM Simulator, but it had an extremely extensive subway system. So pick a simulator version based on these two factors; if it doesn't seem the right capacity, you can always switch it out for a different capacity version. Experience has shown that in large cities, the effects of such a switch may take up to five years to fully manifest. You can tell when things have stabilized by looking at the Traffic Volume Graph in the following way: First, let the game run until there is a sudden shift in traffic patterns. Sometimes, this may take over a year. Then run the game until you go at least a full year without any sudden change in traffic patterns. At that point, the transition to the new capacity simulator is complete.  All this can be done without any harmful effects to your city.

What settings should be used to emulate older traffic simulators?

Please see the User's Guide in the Traffic Simulator Configuration Tool, which was mentioned at the top of this page.   Specifically, the section entitled "Using the Traffic Simulator Configuration Tool to Emulate Older NAM Simulators" addresses this question in detail.

For further questions about using the NAM Simulator, please see the NAM Unified Traffic Simulator and Data View Help thread.

2017 NAM Team