Having cars be "aggressive" in this context basically means they flow into the voids more readily. An example would be moving left into a "this would be an imp

Having cars be "aggressive" in this context basically means they flow into the voids more readily. An example would be moving left into a "this would be an impolite move in any other context" sized cap between two cars to in order to let someone merge and then getting right back out of the lane.