NYSDOT has a fairly extensive chapter in their Highway Design Manual on the subject. They base it on development density - whether or not there are places to walk to and from. Check out the Pedestrian Generator Checklist on Page 18-6.
If you don't want to hang your hat on a state DOT document, you could contact them and ask if they based it on something else, like an AASHTO or ITE publication.
The other reason for sidewalks is safety. Depending on whch study you read, sidewalks will cut the chances of a crash involving a pedestrian walking along the road by 50% to 88% (however, most ped crashes involve people
crossing the road).
If I recall correctly, the ADA doesn't apply to military facilities, but you should check to see if there is a similar DoD policy.
Here is one more resource:
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
"I'm searching for the questions, so my answers will make sense." - Stephen Brust