By reason of the increased duties and responsibilities imposed upon the commission and in lieu of the salaries heretofore authorized by law, the chairman of the commission shall receive an annual salary of fifteen thousand dollars ($15,000) and the other appointed members of the commission shall each receive an annual salary of thirteen thousand dollars ($13,000), payable in semi-monthly installments, solely from funds derived from the Pennsylvania Turnpike System; and each member of the commission shall be reimbursed for the necessary expenses incurred in the performance of his duties.