Surface=fine_gravel - is it for loose gravel or duplicate of surface=compacted

Sounds to me like the English translation of “bombiert” in a road construction context would be the “crown” of a road, or a “crowned” road (in American English at least).
https://www.dirtandgravel.psu.edu/sites/default/files/General%20Resources/Technical%20Bulletins/TB_Crown_and_Cross_Slope.pdf

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