A county board of supervisors may create an authority to operate within the county to carry out this division, or may designate a transportation planning agency designated pursuant to Section 29532 of the Government Code or created pursuant to the Fresno County Transportation Improvement Act pursuant to Division 15 (commencing with Section 142000), or a county transportation commission created pursuant to the County Transportation Act (Division 12 (commencing with Section 130000)) in existence in the county on January 1, 1988, to serve as an authority.