EDIT TO TEXT BELOW: A few days after update 7 there was a new secret patch that they did not list on the update list. After this patch the traffic issues have returned. So ignore the statement I made below because they brought in a new patch that made traffic come back.
There are many traffic related bugs listed so much that I don't want to delete them all. The traffic issue was totally fixed in Update 7 and there is no longer traffic congestion and your sims will use mostly the mass transit. You can have very high populated cities now with no traffic problems. Service, delivery, residential vehicles no longer get stuck in traffic and it removed all problems with trucks not showing up on time and really just totally fixes the game. If you haven't played the game since update 7 then get on it now!