The is a comprehensive technical standard established for the design, evaluation, and rehabilitation of both fixed and movable highway bridges in the United States. Published by the American Association of State Highway and Transportation Officials (AASHTO), this edition refined the Load and Resistance Factor Design (LRFD) methodology, which utilizes statistical knowledge of loads and structural performance to ensure uniform safety across different bridge types. Core Philosophy: The LRFD Methodology

Unlike older "Allowable Stress" or "Load Factor" designs, LRFD is a probability-based approach. It is designed to ensure that the structural system of a bridge can withstand four primary limit states:

Prevents crack growth by limiting stress ranges caused by repetitive loading.

AASHTO LRFD Bridge Design Specifications, 5th Edition - 2010

Accounts for rare but severe events like earthquakes, vessel collisions, or ice loads. Major Revisions in the 5th Edition