Work zone impacts assessment is the process of understanding and managing the safety and mobility impacts of a road construction, maintenance, or rehabilitation project. Assessing WZ impacts is important for developing effective Transportation Management Plans (TMPs) that provide for safety, mobility, and quality while maintaining, rehabilitating, and rebuilding our highways. The Guide presents a general approach for WZ impacts assessment, mirroring the typical program delivery process of transportation agencies. It also provides examples of how agencies are currently assessing and managing WZ impacts, as well as an overview of different traffic analysis tools that can be used for analysis of WZ impacts. The Guide is intended to help transportation agencies in their efforts to make work zones work better, and is the last of four guides to assist agencies with implementing the Work Zone Safety and Mobility Rule (23 CFR 630 Subpart J).