flatbed vs railroad truck

flatbed

noun
  • A railway freight car with no sides; a flatcar. 

  • A document scanner with a flat bed. 

  • An open freight vehicle with no sides, designed to carry heavy or outsized loads. 

adj
  • Having a flat bed. 

verb
  • To transport by flatbed. 

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 flatbed and railroad truck occurred in a corpus of books? (source: Google Ngram Viewer )