system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do cars travel in packs on the highway, even when there are no traffic stops to create groups?
gpt
Faster cars inevitably stack up behind slow cars, generating this pack formation.

Eventually the faster cars will weave through and "escape" until they hit the next pack, but there's always another slow-car-slowly-passing-even-slower-car up ahead to cause another group.

The cars in a group do not stay together long, it's a transient phenomenon that forms and dissolves when cars with different speeds meet.