Games Design Fundamentals - Game Engines: Collision

An example of a game with poor collision is FALLOUT 4. For the most part, the game runs flawlessly with gameplay being fluent and consistently, however, the game’s developer, Bethesda, has a track record of releasing amazing game series such as Skyrim and Wolfenstein that are littered with bugs and questionable choices when it comes to optimization. The cars around Diamond City in Fallout 4 range from being stable props in the player’s immersive experience to being clipping messes that either conflict so poorly with the city’s terrain that it hits and instantly kills the player or, worse yet, explodes into a nuclear cloud, vaporizing everything nearby and leaving dangerous radiation in its wake.

Game asset collisions aren’t defined by the mesh’s surface since having to calculate every poly along the surface of a mesh would be very intensive for the memory and processing power of the computer. Calculations such as calculus and trigonometry are made every frame to simulate physics and without proper optimization, the game's performance suffers.
Because of this, collision is applied to models using primitive 3d shapes such as cubes, spheres, and capsules (cylinders with rounded, spherical ends on either side) so that there’s less to process, resulting in a better running, optimized game.

Collisions in Portal: using a piece of code in the command console, the collision boxes dotted around the game to prevent players from exploiting the courses became visible, showing in a bright pink.