TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 499: Alternate Design/Alternate Bid Process for Pavement-Type Selection documents the state of the practice in alternate design/alternate bid (ADAB) for pavement-type selection by highway agencies. ADAB is a contracting technique that allows the pavement-type selection decision to be made as part of the procurement process. Contractors are permitted to bid their preferred pavement-type alternative using real-time market pricing for the paving materials.