Documentation of statistics: Construction Cost Indices for Civil Engineering Projects
The statistics have been compiled in various forms since 1959, but in its current form the indices for earth work, asphalt work, concrete structures, and iron structures are comparable from 1976 and onwards.
https://www.dst.dk/en/Statistik/dokumentation/documentationofstatistics/construction-cost-indices-for-civil-engineering-projects
Documentation of statistics