You can definitely make the city less traffic-heavy, especially after the DLC. But even in vanilla, for the commute traffic it's mostly a matter of having enoug

You can definitely make the city less traffic-heavy, especially after the DLC. But even in vanilla, for the commute traffic it's mostly a matter of having enough pedestrian bridges and tunnels so that they have uninterrupted journeys, and for the trucks the trick is to place rail depots near industrial and commercial districts so that they never need to get to the highway. Do those two things and you've cleared out most of the problem. Everything else is taken care of by designating a faster arterial road at certain intervals(so that the driving AI's preferences are more predictable) and then designing a one-way flow in and out of areas with a lot of conflict points. It is not exactly how I want to envision my city, but it's also not extremely complicated to work out. The game really limits traffic reduction mostly through the city services, which all have to drive down the roads to provide services.