(d) In lieu of the creation of a county transit and traffic commission in the county where a county planning commission has been established, the county commissioners may, by resolution, confer and impose on such planning commission the additional powers and duties of serving as the county transit and traffic commission, with all the powers and duties conferred by this sub-section upon the county transit and traffic commission. Upon the passage of such resolution by the county commissioners, the terms of office of the existing county transit and traffic commissioners shall terminate and they shall deliver all books, papers, records, furnishings and supplies pertaining to their office to the county planning commission. The passage of such resolution by the county commissioners shall not impair or affect any act done, or right accruing, accrued or acquired, or liability, duty or obligation incurred, prior to the time such resolution takes effect, but the same may be enjoyed, asserted or enforced as fully and to the same extent as if such resolution had not been passed.