If you have not looked at this little gem prepared by Tim Rogers, former NMDoT Bike-Ped-Equestrian coordinator, and Andy Hume, MPO Planner from Las Cruces, you should.
Accommodating Bicyclists through Paved Shoulders on New Mexico’s State Highways 44th Paving and Transportation Conference, Albuquerque, NM. Jan, 9th, 2007.
Wish I had been there.
Here are a couple other useful links. Send more if you got 'em.
FHWA on Shoulder Width
FHWA Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures (safety edge section)
1999 AASHTO Bike Guide