system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it when travelling in a car and sleeping, it seems easier to stay asleep while the vehicle is moving around, but more often than not we wake once the vehicle slows/has stopped?
gpt
a vehicle's movement has a rhythm, and that steady (or mostly steady) rhythm is reassuring to very low-level parts of your brain (the so-called reptile brain). So long as the rhythm continues, your body thinks that you're safe. 

Once the vehicle's movement changes significantly (slowing down, coming in for a landing, swerving to avoid road moose, etc.), you sense the change. That change could be dangerous, so you awaken.