In any county of this state now or hereafter having a population of 400,000 or over, the county board may provide and maintain, at the expense of the county, transportation facilities for the use of the county surveyor and deputies, the sheriff and deputies, and the members of the county board in and about the performance of the duties of their respective offices; provided, that the total amount which may be expended in any one year for transportation of the members of the county board shall not exceed $3,000; provided, further, that the providing of transportation facilities to members of county boards within the provisions of this section shall include and permit reasonable allowances on a monthly basis to members for the use of their own automobiles in the performance of their official duties notwithstanding the provisions of any law fixing allowances for use of their own automobiles by public officers in the performance of their duties on a mileage basis.