Notwithstanding any other provision of this part, before the district may establish any transit service or system which may at any time divert, lessen, or compete for the patronage or revenues of any existing system, the district shall give a written notice to the public utility which is operating the existing system. The written notice shall describe the transit service or system which the district proposes to establish and shall state the time within which the district proposes to establish such service or system.