roadway vs slip road

roadway

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

  • A way used as a road. 

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

slip road

noun
  • A segment of roadway that joins a motorway to ordinary roads (in either direction) 

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