Although many of us are regular drivers, we rarely put much thought into roads. That’s on purpose. If you’re thinking about the roadway itself at all while you’re driving, it’s probably because it was poorly designed.
There are so many factors that go into highway safety, many of which are more philosophical or psychological than pure physics and engineering. But to a certain extent, highway design is an art form. Watch the video from Practical Engineering for more info:
The most appropriate location, alignment, and shape of a highway are selected during the design stage. Highway design involves the consideration of three major factors human, vehicular, and roadway and how these factors interact to provide a safe highway.
A flexible, or asphalt, or Tarmac pavement typically consists of three or four layers. For a four layer flexible pavement, there is a surface course, base course, and subbase course constructed over a compacted, natural soil subgrade.