For the AI profiles, a small set of numbers per driver goes a long way: reaction delay, following distance, how often they change lanes, and how late they brake. Mixing 3 or 4 profiles in the same traffic already reads as "people" rather than "cars on rails".

The thing to watch is fair vs unfair unpredictability. If a car swerves into you with no warning it feels like the game cheated. If it signals or drifts toward the line half a second first, the same move feels like a near miss you dodged. Telegraphing is what makes weaving through traffic a skill instead of luck.