go HERE to google maps
Find Milford Michigan, it'* near the eastern side of the state. zoom in at a decent distance until you can see GM Proving grounds. Once you find it, it'll be a large gray mass on the map (bigger than some towns!), switch your view to satellite instead of map. Zoom in.. You can see all the testing tracks that GM uses! one is a several mile long oval course probably used for top speed. One is squiggled and curvy for handling, and there are some that look like they're used for acceleration testing. There'* some tha tlook like regular back roads so they can test the cars on that too I'd guess. I just thought that was really cool.