Google has added traffic status information to select cities on Google Maps. This is the first substantial Google Maps update in quite some time and it seems as though Google is playing a bit of catch-up with Yahoo! Maps. Yahoo's mapping service has displayed live traffic information for quite some time already.
Regardless, I welcome the new feature.
Google Maps Traffic Info
Yahoo! Maps Traffic Info
For more than 30 major U.S. cities, you can now see up-to-date traffic conditions to help you plan your schedule and route. If you're in San Francisco, New York , Chicago, Dallas, or any of the other cities we now include, just click on the traffic button to show current traffic speeds directly on the map. If your route shows red, you're looking at a stop-and-go commute; yellow, you could be a little late for dinner; green, you've got smooth sailing.
Official Google Blog