Identify U curves in route

I’m trying to identify the mountain roads in a route, and I’ve thought that a good approach could be get the paths with a very closed curve (like a U turn), but now I can not find any documentation about.

Do you know any idea, approx or some documentation or article where this topic has been covered?

The main idea is only know if a route has curve like the image below, or not. For this in my app I’m using PostGIS and Python and data (rote path) comes from OSM.