off-ramp vs slip road

off-ramp

noun
  • A segment of roadway that directs vehicular traffic from a freeway onto local roads. 

  • An exit strategy. 

slip road

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

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