If you set the Traffic Density too high (like... 70 or above? maybe even lower than that), the traffic AI starts to freak out: random cars spawn damaged, the bridge route becomes randomly blocked, any highways get random issues. I'm pretty sure that's not intentional as it doesn't happen on lower density values.
I couldn't reproduce this over 30+ hours of gameplay with traffic density set to 100 (along with view distance and object detail). Using FusionFix 2.5.6 on CE, with the game running at a steady 117 FPS.
If you set the Traffic Density too high (like... 70 or above? maybe even lower than that), the traffic AI starts to freak out: random cars spawn damaged, the bridge route becomes randomly blocked, any highways get random issues. I'm pretty sure that's not intentional as it doesn't happen on lower density values.