The Texas Department of Transportation, in cooperation with local and regional officials, is responsible for planning, designing, building, operating and maintaining the state's transportation system. It works to reduce congestion, enhance safety, expand economic opportunities, improve air quality and increase the value of transportation assets. The department maintains the Texas Transportation Commission, which plans and formulates policies for construction, maintenance, operation and design of the state highway system. The Texas Department of Transportation performs functions related to developing statewide transportation plans that contain various modes of transportation, including highways and turnpikes, aviation, mass transportation, high-speed railroads and water traffic. It conducts and supports a range of programs related to vehicle and traffic safety, litter prevention, transit services, municipal projects, transportation planning, human resources and environment preservation. The department is headquartered in Austin, Texas.