Preliminary phases of project design actually begin early in the project, as an adequate level of engineering design is necessary to be able to accurately determine the feasibility of the alternatives (i.e., whether they are constructible and whether they serve the stated transportation need). Only those alternatives that appear to be feasible will be advanced into environmental documentation. Early levels of design include conceptual design and preliminary engineering. However, following the selection of a preferred alternative for implementation, the project will move into the final design phase. Final design ends with the development of design specifications for construction. During this phase all of the details about how the project will actually happen will be worked out, ending in placing the project out for bid to interested contractors.