Here is the full list of all 12 Urban Trial Freestyle achievements.
Set a 5 star rank in every level
Make 500 flips total
Complete all Challenges
Find all the cash (100.000) lying on the tracks
Complete all tracks in Underground Area
Complete all tracks in Train Depot Area
Complete all tracks in Industrial Area
Finish any track using only acceleration and brake
Crash 100 times
Complete all tracks in Downtown Area
Complete all tracks in Outskirts Area
Complete a track without crashing