Free Radical – Escape a level 5 police chase
A good Point to get the Achievement is at the last Mission for Act 1: Dressed in Peels. There you start the Mission with four Stars, keep shooting police till your at five. Later in the Story you also need to Escape a 5 Star police chase.
There are three easy ways to escape a 5-Star police chase. With the Train, on the Train Tracks or by Boat, just make you you take out the Chopper first (Kill Gunner or Disrupt).