The Chase sequence must be heavily scripted in order to play perfectly (as well as cost-effective to develop.) And I'm not just talking scripted as in writing down, "this happens, they go here, they fight this after this happens...", I mean scripted to what the engine has to handle at any given second and what the characters are doing in the timeline and how long it takes before the sequence is over. The whole thing is probably exactly 8:20 long, every playthrough.
In a fully-developed game, even in a setpiece-type action scene like this, there would be more potential variety and there would be room for the player to make mistakes or have a tough encounter that takes longer to fight than usual; maybe the shooting sections of this fight would just circle around a block or cheat the section of highway a few times if you're bad at aiming or on a high difficulty, then cut to the overpass when you "win". Think of a setpiece sequence in like Uncharted or Gears and you can see that you're inside a linear pipe but you're not usually "on rails".
Here, though, there's little room for anything to go wrong*, because if there were any bug in the game or anything a player could do that might break the game, then the illusion fails, and this demo is all about the perfected illusion that a next-gen engine can present gamers. It would be built less like an action setpiece and more like a pre-scripted cutscene, only this is one where you do have a little bit of control via a reticle and maybe action-triggers (although even those seem to have some scripting.) Once you get to the open-world sequences, then it can have glitches or look like a demo, but until then, it's as on-rails as it can be while still seeming fun and exciting for the "player."
(*Is there even a fail state? It looks like the Agent cars might actually crash even if you don't take them out, especially in the underpass battle they swerve into traffic sometimes without losing control from being shot. I wonder what happens if you don't pull the trigger or intentionally miss?)
So, I bet the car crashes are on a pretty specific vector, following a general script that doesn't really pertain to physics. They swerve one way, countersteer the other way, lose control at the exact same angle, and even flip end-over-end the same number of spins. Maybe there's some room for some variety (moreso in the freeway chase than the shootout under the overpass, since everything is happening behind you and so the game can do something unplanned but still keep going,) and the NPC cars have a little bit of avoidance AI to them when a wreck is happening near them (but they also seem to have have their physics lightened compared to enemy vehicles so that they easily squash out of the way if the Agents need to get past them to attack,) but there has to be a level of control and scripting so that little goes wrong. How those cars break apart when they do crash, how the glass breaks and metal shreds, that's up to the physics system, but the physics system would be given the same few variables of how fast and what direction the vehicle is moving. Easier to design, more stable to run, still enjoayble for the gamer to play, and you only notice how heavily scripted it is on multiple playthroughs or a closer watch.
