Google Maps for Android had been able to provide live traffic data for sometime now. But in the recent update, now it takes into account that information while chalking out optimum route between your source and destination.
You don’t have to do anything to be routed around traffic; just start Navigation like you normally would, either from the Navigation app or from within Google Maps. The latest beta version of Google Maps Navigation, uses the alternative routes that Google Maps always suggests and picks the best one according to the real-time and historical traffic information. That means that Navigation will automatically guide you along the best route given the current traffic conditions.
The feature for now, will just work for North America and Europe as both the Navigation and real-time data are live there.
(via Google Mobile Blog)