Cities: Skylines How to Traffic Guide by drushkey
A couple of really decent guides have appeared and the first one looks at traffic by drushkey. This guide explains how the city has been connected and how the road network within the city has been carefully planned to avoid traffic congestion. If you’re having trouble with traffic take a look at this, it may give you a few ideas.
It’s always a little tougher to sort out traffic retrospectively and it costs more so getting it right from the start will help.