Several articles highlight the SimCity traffic system, the roads, "the arteries and veins of the city" as Tyler Thompson, gameplay producer says, and in particular in this first article, on the blog, entitled the traffic system of SimCity. In SimCity, there are not only vehicles which circulate (one thinks in particular of water, electricity and wastewater without forgetting the pedestrians), however all the circulation lanes agree with the roads (like this is the case most of the time in reality).
On the roads, we see vehicles of all types. Each building has its own vehicles bringing / taking resources, all Sims go to work, run errands and return home. For the city to be functional, it is essential that the roads be optimized to avoid traffic jams: a bottleneck and the beautiful organization can collapse. Again, curved roads provide great flexibility in creation, so cities can adapt to the environment. And above all, players can create unusual cities (see cool cities)!
Sign up for Club Sim for more information on traffic and especially traffic jams! In summary, each moving entity (vehicle or pedestrian) is independent and manages its destination on its own according to different priorities that may change (like a police car, returning to the police station, suddenly called to a crime scene). At each intersection, these entities try to define the best path to reach their destination.
We can see it here, the traffic is not very fluid, these two large lanes are too busy, the traffic jam looms, your Sims will not appreciate wasting so much time in transport, not to mention all the annoying sides (police cars stuck, letting robbers run away or garbage trucks letting garbage accumulate). One solution may be the use of public transport ...