flyover vs footbridge

flyover

noun
  • A high-level overpass built above main overpass lanes. 

  • A road or railway that passes over another, allowing routes to cross without interruption. 

  • A low-level flight, especially of military aircraft, of a ceremonial nature; a flypast (British). 

footbridge

noun
  • A bridge over a road, railway, river, etc for pedestrians. 

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