It shall be the general duty of the city manager to determine the installation and proper timing and maintenance of traffic control devices and signals, to conduct engineering analysis of traffic accidents and to devise remedial measures, to conduct engineering and traffic investigations of traffic conditions and to cooperate with other city officials in the development of ways and means to improve traffic conditions, and to carry out the additional powers and duties imposed by ordinances of the city. Whenever, by the provisions of this chapter, a power is granted to the city manager or a duty imposed upon him, the power may be exercised or the duty performed by a person authorized in writing by him. (Prior code § 3001(b))