All expenses incurred by the board including salaries of employees shall be paid upon voucher forms provided by the office of financial management or pursuant to a regular payroll signed by the chair and the executive director of the board. All expenses of the board shall be paid out of that portion of the motor vehicle fund allocated to the counties and withheld for use by the department of transportation and the county road administration board under the provisions of RCW 46.68.120(1), as now or hereafter amended.