Google is always expanding the coverage of Maps and adding more info to more countries. The latest addition is like traffic data in a couple of new countries as well as more info in some of the places already covered.
"In an effort to make our maps even more accurate and comprehensive, we’ve launched live road traffic in the United Arab Emirates and Kazakhstan. We’ve also expanded live traffic in Brazil, France, Germany, India, Italy, Japan, Malaysia, Mexico, Russia, Spain, and the US!," Google explained
Live traffic conditions are a relatively new addition, the feature has been around for years but only recently started being supported in a larger number of countries.
Google gets data from several sources, including Android phones with Google Maps installed. It uses this aggregate data to judge the current traffic conditions. Obviously, this is easier for the bigger roads and places where smartphones are popular.
Still, as smart mobile devices become increasingly popular, there will be enough data for an accurate estimate in more and more places.