(a) An authority is created under this chapter if a resolution finding that the creation of an authority would be in the public interest and a benefit to persons residing in the county is adopted by:
(1) the county commissioners court;
(2) the governing body of the principal municipality; and
(3) the governing body of at least one municipality other than the principal municipality.
(b) An authority may not be created if the rate of the sales and use tax charged by the city transit department of the principal municipality, when added to an existing sales and use tax collected in the county other than by the principal municipality, would exceed the limit imposed by Section 457.302.