Update: Halo Truck Leads Forza Horizon December IGN Car Pack

[SvennoJ]

Here's a nice article comparing Forza Horizon's version of Colorado to the real thing

http://www.popularmechanics.com/technology/gadgets/video-games/forza-horizons-on-the-real-and-virtual-roads-of-colorado-12824091

The game has 216 distinct roads. I can't share every detail about the map Turn 10 provided to help me on the drive, but it starts in Denver, stretches west toward Glenwood Springs, dips down to Paonia and then to Grand Junction (and the Colorado National Monument), heads south toward Telluride, then east toward Colorado Springs. It's well over 1000 miles of reference material, and I probably drove about 700 miles of it.

The guys at Turn 10 Studios didn't simply re-create this one major highway, though. Driving on an Xbox 360 isn't driving a real car, and even with these stunning vistas, players would have gotten bored. Ralph Fulton of Playground Games, a design director for the game, tells me that gamers expect scenes to change about every 3 minutes, not every 30. So Forza Horizon includes many of the highway scenes I drove through, but condensed for the Xbox experience.

Some of the best scenery in the game, though, is on the northeastern side of the map, a bit south and east of the fictional town of Beaumont. Fulton told me this is based on reference material collected near the real town of Paonia, Colo., and the Paonia Reservoir. You'll find tunnels, road-side barns, and raging waterfalls rendered perfectly.

I don't agree with the "gamers expect scenery to change every 3 minutes" sentiment though. I find the highway section quite short and most of the areas in game quite small. 6 minutes to go from 1 corner to the other makes free roaming a bit underwhelming.
Hopefully they'll make a bigger map for the sequel. My longing for real driving in a TDU style real world map goes on.