goods wagon vs railroad truck

goods wagon

noun
  • A railway wagon for carrying freight. 

railroad truck

noun
  • A chassis or framework-like structure underneath a railroad car to which wheel axles (and, hence, wheels) are attached through bearings. (Not to be confused with railway truck or railtruck, which are British English synonyms of railroad car) 

How often have the words goods wagon and railroad truck occurred in a corpus of books? (source: Google Ngram Viewer )