parking lot vs slip road

parking lot

noun
  • A road blocked by stop-start traffic. 

  • An open area, generally paved, where automobiles may be left when not in use. 

slip road

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

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