Geotechnical engineering analyses and designs for transportation structures have traditionally been based on Allowable Stress Design (ASD), also known as Working Stress Design (WSD). Transportation structures that require geotechnical engineering are bridge foundations, sign and lighting foundations, earth retaining structures (MSE walls, reinforced concrete walls, brick walls, cantilever walls, etc.), and roadway embankments (at bridge approaches and along roadways). The primary guidance for the ASD design methodology has been the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges (17th edition – last edition published 2002) and various Federal Highway Administration (FHWA) geotechnical engineering publications.