Resistance 3

Replay Chapter: Mt. Pleasant, PA: Train Defense
After defeating the giant Chimera in the coal mines, you will gain access to a train. Once the scene ends you will be given the task of protecting the train from hijackers driving jeeps. Now, instead of destroying the vehicles, you should use the Carbine, Deadeye, or Marksman to shoot the driver, not the vehicle. Simply wait for the vehicle to come into range, headshot the driver, and the vehicle will crash itself. Rinse and repeat until you have 5.

You don't need to get all 5 in one session. You could get 3 on your first play through, then 2 more on another playthrough or through chapter select, or any combination. It won't have any effect on the trophy. You can also farm this at checkpoints. Kill 2 or 3 drivers, then allow them to kill you. Your progress towards the trophy will be retained, but the drivers will respawn. Either way, once you have killed 5 drivers, the trophy will unlock. You can track your progress through the Rewards tab of the Extras menu.

For a great video by sunnygrg demonstrating this trophy, see below: