Autobahn Polizei

If you don't earn this by the end of your story mode load up patrol and spawn at "Stadium - Center" with the Tribun. Race around the track until you get to the jump in the middle that requires about 80km/h to clear. With the Tribun and the respawn trick you can do this jump multiple times per minute. Quick way to finish up your remaining jumps. Hope this helps

Simply involves becoming airborne, either by ramp or other means. This will pop naturaly through the course of the game.