Morning Commute...
As a general rule of thumb, if your commute involves a bridge or tunnel, you'll probably be in traffic. The most severe morning traffic occurs inbound to the city from the eastern and western suburbs. Both can back up pretty severely through their respective tunnels. Google's "typical" traffic map is a great tool to understand what to expect for your morning commute.
Evening Commute...
As is the case with he morning commute, avoid bridges and tunnels if possible. This can result in a maze of residential roads, but in some cases, avoiding the highway delays is rational justification. It's also wise to avoid crossing through the city during the evening hours, starting about 3:00 pm, particularly traveling westward. Google's "typical" traffic map is also useful to understand your evening commute.
