system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is the speed of vehicles traveling on a highway monitored by aircraft?

I went on a road trip recently and on the way there were signs that say speed monitored by aircraft. How does this work? Are drones used? Some type of plane/helicopter or even a blimp? Is it more accurate/effective?
gpt
Lines are painted 1/4 mile (or possibly other distances) away from each other across the highway. A plane flies above the marked area with officers who will time cars from point a to point b. He/she will then radio down to patrol cars the location, color, and model of the car, and the calculated speed based on the time it took them to travel from a to b. It's generally not used as its pretty expensive to keep the planes up in the air.