Question on construction of cut slopes

[brcuzz]

While driving the highways and byways of our great nation, I've been marveling at how smooth, planar, and plain these steep slopes are, cut into native soil and rock. The gradients are, to my understanding, typically 2:1 or a 50% slope. My question is: How are they constructed? Surely a motor grader can't side slope on a 50% grade with any safety or efficiency if it's even possible for a dare. So how are these cut faces made?

 

[EireChch]

A nice big 40tonne excavator.

The start at the top and work there way down bit by bit and shape as they go.