C-Bear
Don't know what you are looking at, but my current working copy of Florida Statutes Ch 316 et sec list those dimensions as dead on in accordance with the 2014 publication date.
Also, the Federal Highway Administration Compiled Regulations for highway design list 13'-6" (13.5') as minimum overhead low point clearance for Federal Aid Primary and Secondary roadways and recommended for all numbered State and County Routes. (Overhead clearance less than 16'-0" must be clearly marked according to the UMCTD.)
Are you dealing with some other government?