All flights in 24 hours are put in that specified time slot. There should have been numerous collisions as everthing in 24 hours presented at a given time. But here, nothing to do with collision avoidance. They are just presenting the trails left by all the flights.

The real collision avoidance is done by Air Traffic control from the ground base and mid-air collision by the Traffic Alert and Collision Avoidance System (TACAS) installed in each aircraft. With this it comes as if you don't plan any collision avoidance in advance before taking out your car into the roads.

It could be same in flights. The difference is that they sense larger proximity space. I am not sure if they have overall collision avoidance control base in advance. I believe, every aircraft are resposible to keep itself updated about flights in its proximity. It has nothing to do with flights several hours distant on its route unless it senses.