system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are manhole covers not in the middle of a lane so car tires don't run over them?
gpt
Transportation engineer here. Usually the sewer systems under the road are much larger than you would think. Usually 10-30 ft wide. If you think of a cut-away of this underground sewer (essentially looking at it as though it's a really large pipe so you are thinking of It as a circle in cut-away view), it makes most sense to put the manhole at the top most part of the sewer (top of the circle). Now, roads get re-surfaced all the time. Curbs and lanes change due to the needs of traffic. That sewer system most likely has been there for a long time if there has always been a road there. Even in new construction, there was probably an older sewer system in place for many years. Cost wise, no way are they going to go with the hassle of relocating a manhole when they can just level it as best the can. Sometimes the contractor does a bad job with this and you get your pothole-like manholes. But relocating means a lot more engineering and subsurface work. It would be nice to do, but it's usually just not in the budget for that type of jobs. 

Other times during new construction, the contractor putting in the sewer and the contractor putting in the road just miss their mark slightly. Most of the time, they're given basic plan sets with only their part on it. And usually it's different contractors for different aspects. 

Hope this helps.