There is a large wealth of information readily available to the public on the USFS website; it just takes a bit of digging, and a lot of reading, to understand what is there. The first place to start is the official Trails Managment Handbook. This is a 35 page document that explains start to finish the way trails should be managed in our National Forests.
Want to know the black and white definitions of a Bicycle? Climbing Turn? Switchback? Trail? Here you go.
This document goes into details on parts of trail management that are covered in a more visual fashion on other parts of the USFS website. Bottom line is that this is an essential resource for understanding how the USFS should manage trails, and it should be a mandatory read for volunteer trail groups.
PLEASE NOTE: Much of the above has been directly copied from referenced sources publicly available on the internet. Subjective opinion and interpretation can be found in color-hilited text boxes.