The more vehicles you use as traffic, the more unrealistic it gets imo. This is due to the cars driving at random speeds in their lanes and not going faster in the left lane. This can be annoying if you're stuck behind 2 cars going the same speed for ages. Furthermore it would be cool for cars on the left lane to move out of the lane when you drive close up to them/ honk/ flash lights so they don't block it all the time. Would be great for realistic driving
