Additional to server issues, Maxis is working on SimCity patch to fix traffic jams. The problem is vehicles tend to take the shortest possible route between destinations.
“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 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.”
Additionally Maxis is slowly re-enabling some of the non-essential features that we had turned off during the week of launch. Regional Achievements are live on a select number of servers and re-enabled Leaderboards on the Test server.
Maxis asks willing players to join the Test server in order to “expedite the timeframe in which brought back to the rest of our servers.”
Source: SimCity Blog