Watch Dogs "Free Radical" Achievement Guide: Escape a Level 5 Police Chase

The best time 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. There are two easy ways to escape a 5-Star police chase. With the train or on the train tracks, the important thing is that you kill the chopper (you only need to kill the gunner), then you can just ride the train or drive on the train track away.