solarpunk memes

Not even that. The plans existed beforehand, and what the Nazis built was largely useless in war as rail logistics were way more important and the network was rather incomplete. What the Autobahn did enable, though, was the quick advance of allied troops. Parts of the Autobahn were also used as military airports which is why you see the current-day Autobahn make a weird curve around Ramstein Airbase. Those still exist but unlike in the cold war it's not airbases that can pop up within days but sections of paved median, with the barriers separating the directions being easily removable. That is, the runway is mostly in place, the rest would have to be constructed, OTOH it's dirt cheap to do.

Mostly, for the Nazis, it was a works programme. Millions of unemployed were put to the task under quite bad working conditions, the workers then wrote letters to the Führer portraying the bad, "Ungermanic, dishonourable" behaviour of their bosses, those letters never reached Hitler they reached the GeStaPo. C.f. "Wenn das der Führer wüsste".

Oh, EDIT, there's one good thing that came out of Nazi rule: They pushed full-grain bread, preferably rye, heavily. The whole ideology behind it was Nazi-typical bonkers, also preparation for a war economy, but the idea in general is definitely a good one and Germany kept its preference for at least partly full-grain as well as rye-heavy breads.