The amount of the coins required to be deposited in parking meters, as provided above is levied and assessed as a fee to provide for the proper regulation, control and inspection of traffic upon the public streets, and to cover the cost of supervising, regulating and inspecting the parking of vehicles in the parking meter zones provided for herein, the cost of placing and maintaining lines or marking, designating parking spaces in parking meter zones and the cost of the purchase, supervision, protection, inspection, installation, operation, maintenance, control and use of the parking meters installed hereunder, and the special fund in which such fees shall be placed shall be devoted exclusively to those purposes, except as provided by the Charter.
(Rev. Code 1954 § 6515)