Some racing games like TrackMania and ModNation Racers tout the ability to create custom tracks but Ridge Racer Unbounded is taking the concept one step further by letting players make their own custom cities. Unbounded's "Create or Destroy" trailer doesn't quite go into the specifics of city creation but demonstrates racers are free to cause as much damage as they please in whatever urban locale they're speeding through.
Unfortunately, how much control players have with creating their cities is not known right now. The trailer seems to suggest anyone can edit street layouts, building placement, and include minor details like landmarks and underpasses. At least you can share your creations online.
Ridge Racer Unbounded releases in 2012 for Xbox 360, PlayStation 3, and PC.