Unity 3D Engine
http://unity3d.com/unity/download
http://blogs.unity3d.com/2010/04/24/car-tutorial/
http://www.unityracingkit.com
Delta3D - GeekLog
OpenStreetMap
data from OpenStreetMap, some digital elevation model (heightmap), satellite imagery for textures, and cook a racing/cruising game where I could drive around familiar parts of the city.
http://www.youtube.com/watch?v=VLTBYmmvLus
http://download.geofabrik.de/europe.html
Elevation Data
http://www.viewfinderpanoramas.org/dem3.html
http://www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm
Convert to Heightmap
http://www.crydev.net/viewtopic.php?t=9158
https://alastaira.wordpress.com/2013/11/12/importing-dem-terrain-heightmaps-for-unity-using-gdal/