The provisions of §22-73 shall not prohibit:
A. Emergency Vehicle. The operation of emergency vehicles upon any street in the City;
B. Public Utilities. The operation of trucks owned or operated by the City, public utilities, any contractor or materialman, while engaged in the repair, maintenance or construction of streets, street improvements, or street utilities within the City;
C. Detoured Trucks. The operation of trucks upon any officially established detour in any case were such truck could lawfully be operated upon the street for which such detour is established.