The 2009 AASHTO Transportation Glossary is an update and revision of the 1983 Transportation Glossary and the 1998 Transportation Glossary, which was unpublished. The largest additions in terminology were in bridge and drainage subjects. The new Glossary also includes lists of organizational acronyms, abbreviations, and other glossary references. Terms and definitions in this glossary were taken from an unpublished 1998 AASHTO Glossary and supplemented with definitions listed in AASHTO publications issued after 1998. Several additional sources were also referenced, including the Highway Capacity Manual, Manual on Uniform Traffic Control Devices, Code of Federal Regulations-Title 23, an FHWA list of roundabout terminology, and the Transportation Research Thesaurus. Glossary terms are listed in alphabetical order regardless of transportation mode. However, the glossary also includes two indexes-subject area and keyword-which provide cross references for the user.