title: OpenLayers apply style to only part of a road
body: <p>I want to make a map that represent the traffic for a city. So I have some traffic metrics that I want to visualize on the map. I wish to color each road different colours depending it's current traffic.</p>
  
  <p>Something like that:</p>
  
  <p><img src="https://user-images.githubusercontent.com/17817424/51060531-0b5b1980-15be-11e9-93fb-39e652217fb5.png" alt="image"></p>
  
  <p>I tried to find a tutorial on how to apply style to only part of a roads, but I could not find how to do that.</p>
  
  <p>Thank you very much it will help a lot thanks!!</p>