roadway vs viaduct

roadway

noun
  • The portion of a bridge or railway used by traffic. 

  • The main or central portion of a road, used by the vehicles. 

  • A way used as a road. 

viaduct

noun
  • A bridge with several spans that carries road or rail traffic over a valley or other obstacles. 

How often have the words roadway and viaduct occurred in a corpus of books? (source: Google Ngram Viewer )