Variable pitch axial flow fans for application in vehicular tunnel ventilating systems are described. The fan design is of German origin and is considered to represent the state of the art, matured over more than two decades of operating experience. Its use for tunnel ventilating systems in the United States appears to be justifiable. The design and performance are described. Three major areas--energy conservation, space requirements, and number of pieces of equipment--provide the largest savings potential and make this fan design most attractive.(Author)