Complex projects involving new, expanded, or relocated highway facilities require a location study. Public involvement and comment are actively solicited during the location study and subsequent environmental document preparation. The location study determines the most advantageous mode (highway, light rail, train, bus, etc.) or combination of modes to solve a transportation problem. If the mode selected is a highway, the location study also recommends a location (alignment) and the type of facility (2-lane, 4-lane, freeway, etc.) to be constructed, based on engineering and environmental constraints. Information from the location study is incorporated into the environmental document [environmental impact statement (EIS) or environmental assessment (EA)] that must be prepared for the project. The district offices conduct location studies, with headquarters staff assisting in the analysis of the purpose and need for the project and the selection of a preferred alternative.