This document is the Work Zone Data Dictionary (WZDD) Report, developed as the primary deliverable for Task 4 under the Federal Highway Administration (FHWA’s) Work Zone Data Initiative (WZDI) Project. It describes the methodology and components included within Work Zone Activity Data (WZAD). This document supports the desired WZAD elements identified during stakeholder outreach discussions under Task 2 of the WZDI and documented in Work Zone Activity Data Needs and Opportunities (FHWA-XXX-XX-XXXX). It also includes traceability to data flows detailed under the Task 3 companion document, Framework for Work Zone Activity Data Collection and Management (FHWA-XX-XXXX). It is not meant as a prescriptive database nor does it profess to contain all the data that are needed by each individual data provider or consumer. Rather, it is composed of work zone-related data concepts driven by industry needs. It attempts to specify consistent data with respect to meaning and enumerated values. Its contents may serve as a reference to organizations developing their own Work Zone Data Systems (WZDS) particularly in areas that vary significantly from organization to organization such as assignment of locations (e.g., begin / end locations), temporal states, and impacts. Additionally, this document is set up to enable WZDS to adopt data concepts as they are ready or as specific stakeholder groups are incorporated into the data environment. The migration and rollout approach is described in the Work Zone Activity Data (WZAD) Guidance Document (FHWA-XXX-XX-XXXX).