Google is expanding its traffic layer to cover all U.S. highways and arterials when data is available. It takes almost zero effort on your part just turn on Google Maps for mobile before starting your car. The more people that participate, the better the resulting traffic reports get for everybody. Google is fortunate to have a lot of people using our products, and that scale helps make our products better. We only use anonymous speed and location information to calculate traffic conditions, and only do so when you have enabled location services on your phone.”]
Source: https://googleblog.blogspot.com/2009/08/bright-side-of-sitting-in-traffic.html