system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: How do those traffic counters (the black hoses across the street) work? How can they tell an 18-wheeler from a car?
gpt
Short answer: they don't need to. 

They are trying to figure out how much the road is *used*, not driven on. Obviously an 18-wheeler puts more wear on it than a motorcycle. A simple way to approximate it is just by how many tires cross the road.