What happens when you improve the road system of a city?
You get citizens perishing of water pollution at an incredibly alarming rate. This is an interesting curveball that I did not see coming, and absolutely diminished my city's population. From a peak of 52,000, you can watch the population plummet to less than 20,000 all in one video.
I fix it by demolishing some old water pumps and replacing them, but it is pretty absurd how quickly people left in droves.
This was a fun video where I learned new things about the impacts of Pollution, and large industrial zones.