Go to the Cheats menu and enter these codes:
Cars are indestructible:
Unlock all cars:
Make cop cars weaker:
In order to unlock this option in the Cheats menu, you'll need to rack up 666 miles on your odometer. Once you do that, simply go and switch it on. In the game, you can switch character models with any pedestrian by melee attacking them.
Golden Star Unlockables
Collect the golden stars found all over the map to unlock these secrets. There are 50 in each era, but they unlock the same things in the same order.
10 Stars - Health Upgrade
20 Stars - Nitrous Upgrade
30 Stars - Double Ammo Capacity
40 Stars - Double Car Durability
50 Stars - Free Vehicle Upgrades
Game Completion Unlockables
Simply beat the game to access: Atlus Racer, Negotiator Vehicle, Ram Raider, Then and Now Option (Change Era at will).