Authorised Training Centres - India - Maharashtra. Bridge Inspection Definitions - Subcommittee on Public Affairs. Annual Average Daily Traffic (AADT) The total volume passing a point or segment of a highway facility in both directions for one year, divided by the number of days in the year. Abutment A retaining wall supporting the ends of a bridge or viaduct. A merican A ssociation of S tate H ighway and T ransportation O fficials (AASHTO) Australia Civil Engineering Courses Australia Training Degrees Studies Programs.