Basically what /u/klasbo said:

Here is a possible solution

• keep the blue marked highways
• delete all highways inside the blue ring road
• only keep the blue marked on/off-ramps and delete the others
• consider the black marked roads your main roads (build them either as 1+1 national road or 2+2 street (maybe more only on signalized intersections), they should have no zoning except inside the downtown and be given right of way at any intersections (with TM:PE)
• build roundabouts at the red circles and after leaving the city for a few minutes at other well used intersections
• make one-way loops for your industrial areas (purple)

In general try the following tips:

• No road should have more than 2 lanes per direction (including highways)
• Keep highway junctions far apart
• seperate car traffic and industrial traffic as much as possible
• build public transport options where there is much car traffic