This is a great analysis but it does focus exclusively on ‘roughness’, which is obviously important but isn’t the be-all-end-all of road quality.
One area I notice in particular that roads in the northeast US subjectively feel worse than Europe is in quality of road markings. Constant plow scraping and harsh salting seems to destroy markings.
I think it also shows up in the overall fit and finish of road infrastructure - edging and barriers, signage, lighting, maintenance of medians, how curbs and furniture contribute to junction legibility… and of course bridges.
One major reason is that European countries typically have national road agencies and consistent standards across the country (because, generally, smaller and less federal). US’s patchwork of federal, state and local road maintenance leads to vastly different budgets and department priorities across the network.
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