Calculate and document that an open-grid pavement complies with a 50% unbound?

Hello, 

This will probably vary depending on the product/design being used. If your system is in units, I would look at the product info (cutsheets, etc) and the % breakdown in a single unit between bound/unbound, which will give you an idea of the whole. You should include an explanation for the reviewers and show a calculation of how you arrived at the final SF total that you'll use in the credit documentation.

I have not had to do this calculation on one of my projects, yet, but have had similar instances elsewhere where the methodology for calculating something wasn't provided in the Reference Guide. In those instances, if I am not confident in my assumptions, I often contact GBCI through their webpage (http://www.gbci.org/contact), explain the approach, and ask if it is appropriate. They should be able to confirm if your approach to calculating things is appropriate, but will not be able to tell you if it will be officially accepted, if that makes sense. To confirm acceptance, you would need to submit a CIR.