In any city with a population of seven hundred thousand or more as shown by the last federal census, which by action of the legislative authority establishes within the police department a unit assigned to the control of traffic, a member of the police department of said city who is appointed the head of such unit by whatever title designated, shall not be subject to competitive examination, notwithstanding section 124.44 of the Revised Code. The status within the uniform ranks of such member while serving as the head of such traffic unit shall remain unchanged and notwithstanding the compensation fixed for such position, he shall not acquire any right to promotion other than such rights to promotion which apply to the rank held at the time of appointment as head of such traffic control unit.