We can simplify this further.First upgrade the side streets to avenue status.Second download the ninja boulivard station from the lot exchange if you don't have it...the high capacity one is my favorite.Third use them everywhere.Fourth invest in RR/subway lines.Yes always put commerce close to residential areas.I like placing Landmarks that employ lots of people at opposite sides of residential areas to split up the traffic.If they are close enough(10 squares or less) to residents you will notice something..residents will walk to work.