Thanks for playing! Great feedback!
Yeah, we definitely had some performance issues. It ran silky smooth on my machine, but I didn't think to test it on other machines. Lesson learned. Next game I'll put in some frustum culling or distance culling. No need to be calculating all the A* pathfinding for NPCs offscreen.
The cars spawn enemies at intervals, so there's some progression, but it's not obvious to the players, so it might as well not exist as a mechanic.