18-wheeler vs freightwagon

18-wheeler

noun
  • A big rig truck: a semi-trailer plus the truck or tractor pulling it. 

freightwagon

noun
  • Any vehicle, such as a cart, wagon, lorry, truck, or boxcar, used for carrying or transporting goods; a cargo truck. 

How often have the words 18-wheeler and freightwagon occurred in a corpus of books? (source: Google Ngram Viewer )