SIMCITY’S HEAVY TRAFFIC
September 20, 2012
Guillaume Pierre, Lead Gameplay Scripter
Hello SimCity Insiders! I’m Guillaume Pierre, Lead Gameplay Scripter on SimCity. My team & I build the game’s simulation using the GlassBox Engine. If you have not done so yet, I recommend you read Tuesday’s blog postabout public transit options. Today, I’m going to talk about emergent traffic.
Previous SimCity games took a map approach to traffic, where each cell would define its maximum traversable speed, along with its traffic capacity and what types of vehicles (pedestrians, cars, etc.) can go on it. In the newSimCity, however, we have actual vehicles that follow the roads, wait at lights and get stuck in traffic. They are path-bound agents that have to make decisions about where they should go, both on a strategic and tactical level.
On the strategic level, each agent is given a list of destinations it should go to, sorted by priority. For example, when Sims decide to go to work, the list goes: 1. Go to work, 2. Go back home, and 3. Leave the city.
Avenues like this help alleviate heavy traffic.
As the Sims leave their homes (either by foot if the destination is close enough, or by car if it’s farther out) they will try to go to the closest destination at the top of the list. At each intersection, the Sims will try to take the best path to the destination, based on distance and on how many workers are needed in shops and factories. If for some reason the top destination becomes unavailable, then the Sims will try to go back home.
Some agents may switch back to the top priority when it becomes available again, while others will only go down the list. For example, the first option is used by police cars that may be patrolling the streets and then all of a sudden need to drive to the scene of a crime, while the second option is suitable for large crowds that need to be more consistent with their destination.
On the tactical level, cars will try to go into the correct lane before reaching an intersection, so if workers need to make a left turn to reach a coal mine, you’ll see a bunch of vehicles queuing up on the left side of an avenue, while the middle and right lanes may only have light traffic. As a city planner, you really need to think about how your Sims can most efficiently get to their destination.
Another thing to consider when building your city is how long cars will have to wait at intersections. Cars on an avenue will wait a shorter time at a red light than the cars on a four-lane road that’s crossing it. Emergency vehicles on the other hand will force the lights to turn green in order to get to their destination faster, potentially causing more traffic for Sims going back home after their work day.
There’s a lot more to say about traffic, but that will be it for today. Come back again soon for more exclusive information in SimCity Insider!