Naga, I had a look at your pic. I suggest you take a few moments to follow a couple of cars. You will find that cross-roads are a major hold-up compared to T junctions.
Also watch behaviour on avenues. Cars will frequently go around in circles between junctions. They travel along the road until they reach a junction, do a u-turn and return the way they came. I have counted 5 circuits with a single car. Obviously, they don't do this all the time, and when they do, once or twice is more common, but this is really a problem on a busy road.
The other point with avenues is that cars can only turn right out of their house. This can cause problems with the repeated circular behaviour. However, this can also be used to your advantage if you wish to force traffic in a particular direction. I suggest you give it a try. Use avenues for major routes and then streets joining the avenue with a T junction. Place your houses along the street, not the avenues and you will really notice the difference. This is especially functional if you use a large rectangle or elongated oval from the main entrance. (Just wide enough to take two full sized buildings) and then place your commercial buildings, tourist attractions, bus depots etc. inside, with no roads cutting through the loop. This keeps the inside lane of the avenue free from junctions and flowing reasonably smoothly. It also concentrates the outside traffic and keeps it from blocking routes for your in town vehicles.
If you then use street cars and park and rides on the avenue you will further reduce traffic and increase flow rate. Finally, place your power plant close to the your left of the entrance to your city and your storage depots as close to the entrance as possible. A single, no exit, road will handle this best, if you can. Using this formula, I have several 200k cities working smoothly. Can't do anything about the traffic cues on the motorway outside though.
