The department shall be responsible for developing a specific and long-range state highway system plan. The department shall annually formulate plans to meet the state highway system needs of all facets of the state and shall assign priorities for such needs. The department shall, on or before December 1 of each year, present such plans to the Legislature. The plans shall be referred to the appropriate standing committees of the Legislature for review. The department shall consider the preservation of the existing state highway system asset as its primary priority except as may otherwise be provided in state or federal law. In establishing secondary priorities, the department shall consider a variety of factors, including, but not limited to, current and projected traffic volume, safety requirements, economic development needs, current and projected demographic trends, and enhancement of the quality of life for all Nebraska citizens. The state highway system plan shall include the designation of those portions of the state highway system which shall be expressways.