This major group includes general contractors primarily engaged in heavy construction other than building, such as highways and streets, bridges, sewers, railroads, irrigation projects, flood control projects and marine construction, and special trade contractors primarily engaged in activities of a type that are clearly specialized to such heavy construction and are not normally performed on buildings or building-related projects. Specialized activities that are covered here include grading for highways and airport runways; guardrail construction; installation of highway signs; trenching; underwater rock removal; and asphalt and concrete construction of roads, highways, streets and public sidewalks. Establishments primarily engaged in specialized activities that may be performed on buildings or on other heavy construction projects are classified in Major Group 17. These include contractors primarily engaged in painting (including bridge painting and traffic lane painting), electrical work (including work on bridges, power lines, and power plants), and carpentry work.