milepost vs turning point

milepost

noun
  • A sign or post beside a railway marking the distance from the (actual or nominal) start of a line (usually the principal terminus or junction with a more major line) 

  • A post on a highway, often with one or more fingerposts, showing the distance in miles to nearby places 

verb
  • To place mileposts along (a road, etc.). 

turning point

noun
  • A crossroads. 

  • A T-junction. 

  • A decisive point at which a significant change or historical event occurs, or at which a decision must be made. 

  • A maximum or minimum on a graph. 

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