This is a good read, it discusses how they are going to improve the traffic system!
We understand that when cars always take the shortest route between point A and point B there will be unavoidable (and illogical) traffic jams, so we are retuning these values it to make the traffic flow more realistically. Guillaume Pierre (our lead scripter) talked a bit about the improvements that we are making to the traffic system in the game here. To dig a little deeper our roads will have a weighting system based on 25%, 50% and 75% capacity. As a road hits those marks it will become less and less appealing for other cars, increasing the likelihood of them taking an alternate path if one exists.
Full Blog here: http://www.simcity.com/en_US/blog/article/simcity-update-8