autoblock vs slow train

autoblock

noun
  • A technique used in rappelling and ascending, with a friction hitch around the climbing rope. 

  • (An) automatic blocking (inhibition of a feature etc.). 

verb
  • To automatically block. 

  • To use the autoblock technique. 

slow train

noun
  • The act of doing something (possibly, but not necessarily traveling) slowly. 

  • Synonym of local train 

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