Check out the traffic flow state in Belgium where measured (15min window). I went ahead on the concept and built a real one, while building a mobile HTML5 application. You can see the page full size here. Click the house , bottom right to zoom to the max extent of the traffic layer.
Since a few months I dove into the mapping thing like a mad man. Having access to tons of geodata makes that really fun and rewarding. Playing with JOSM I’ve really wondered why they could use aerial imagery Bing data for OpenStreetMaps. So I went to search for what the licenses where all about.