The huge retaining wall in the photo above is one of probably thousands across the United States. We take such things for granted as we drive along the Interstate, and often don't consider them or even notice them. If you have looked through other pages on this website, especially ones pertaining to residential walls, you should be able to appreciate at least one vital aspect of such mundane structures; by and large they function perfectly, and don't crack or pitch out!
This partcular wall is perfectly flat, yet it's probably at least 30 to 40 feet tall at its highest point. Being that this section of Interstate five was built in the early to mid 1960's it's safe to assume that this wall is at least 45 years old. Whatever they did, they did correctly!
What I suspect, but cannot prove, is that the wall is very thick, utilizes high quality concrete, and incorporates extensive use of rebar. In addition, I suspect that the wall is set into the ground to a significant depth, to help prevent the kind of tipping out of plumb seen in many residential retaining walls.