The behavior of traffic in SimCity has been a source of major criticism since the game's release earlier this year. Update 7 will further improve this, hopefully making SimCity's drivers appear a little more sensible. According to Software Engineer Alexander Harkness, Update 7 will result in less clumping together of vehicles in your cities. The artificial intelligence regarding traffic routing, which was terrible to begin with, is being further tweaked too, which should mean less traffic jams.
You can see how Maxis have brought bridges and roads to SimCity in the video below. Guillaume Pierre explains how they work, and you can see how this is another way you will be able to decrease congestion in your crowded city.