The bus routes I never really got the hang of - I'd setup a few routes running through the outer ring of my city, and then going through the middle - but it hardly seemed to be used.
There are two keys to reducing traffic.
1 - mass transit.
Metros join areas together and move a lot of people. Buses distribute to and from metro stations and all around.
Since there are two directions to a subway tunnel, I like to put them into loops and have some loops overlap, but going in the opposite direction, so that the trains stay on their own loops and don't interfere with each other.
In the stellar diagram below, I've got subway represented by the thick coloured lines with stations in black. There are four lines, the red being the main loop around my high density residential core. The other lines go somewhere else - commercial or industrial. Within each of those other areas, I have bus routes (thin grey lines) picking up passengers from outside the metro stations and depositing them around various areas and also dropping them off at the metro stations.
I've also got a lot of walkways linking up areas leading to areas, especially to bus stops and subway routes.
So if a cim wants to get from the bottom left of my map the the upper right, he walks to a bus stop, buses to a metro station on the yellow line, switches trains on the red line, switches again on the green line and then catches a bus from outside a green station and finally walks a hundred metres to his desitination.
2 - give industrial lots of road infrastructure.
Keep industrial separated as much as possible. Trucks should go onto the highways and not through towns. If you have direct links between industrial to the other areas and you find that heavy trucks use them, zone areas around those links and put a heavy vehicle ban on them to force them to go to the highway. If you want to get goods to your commercial area quicker, you can put in rail freight terminals near industrial areas and near commercial areas, but give them plenty of room as the ones near industrial areas will create a lot of heavy vehicle traffic. The ones near commercial should generate lots of delivery van traffic, assuming you have demand for it in commercial.
Industrial areas are where you apply most of the traffic management tricks as it's the hardest to control. In my city, the original industrial area was rezoned to commercial and I now have two industrial hubs well away from the others. You can keep industrial areas smaller to avoid a lot of the problems - link little areas to the highways rather than have one massive industrial area.
