Danger Zone

This will very likely come naturally when playing your way through all of the Test Phases and wont require any simulations to be replayed. Before you begin any crash simulation, you will see a display to the bottom left of the screen of the score requirements for the level. The first time you obtain a Gold Medal you will unlock the trophy.

See the link in the Roadmap, for videos showing a Platinum Medal being earned for every simulation of every Test Phase if you're having any trouble.