Instructions
Create extra zones. Build about a 2:1 ratio of low industrial and medium residential zones.
Expand roads. Since the mission focuses on average traffic level, providing more roads for residents to use will lower the amount of congestion on each road.
Use as few intersections as possible to the zones with roads. Intersections create congestion by stopping the flow of traffic. The faster traffic can move, the fewer people will be stuck on the road. Use the feature to build curved roads to eliminate the need for intersections and traffic lights.