I'm working on updating my bridge book now. There are some significant changes, so may need 7th edition. There will be 12 new pages in my book that goes through these changes, but some are so extensively that you would need the new code. It did affect 2 of the problems in my book (1 vertical and 1 lateral) that will be updated.
Also, may want to poke around online and see if a pdf can be found. A link was posted to this forum for a previous AASHTO code.