system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Average speed cameras

If the purpose of average speed cameras is to measure your speed between one fixed point and another fixed point, why do they need to have so many cameras in between? Why not just have one at the start, one at the end and one at each exit point in between?
gpt
Pretend you have 2 cameras, 1 at mile marker 0, and the second at mile marker 1. 

At 60 mph, it should take you 1 minute to cover that distance. But what if you drive at 80 mph for the first 1/2 mile, then get stuck in traffic and go much slower for the remaining 1/2 mile? You were speeding at some point in that 1 mile gap. 

A third camera at the 1/2 mile point would have caught you. Plus what if maybe a semi-truck was in the way, and blocked the camera from seeing your plate at the first camera? Or maybe the sun's glare made it hard to see, etc 

More cameras, more chances to nab you.