Section 17. The colonel shall forward to the secretary of public safety and the commissioner of administration his estimate of expenses for the department as required under section three of chapter twenty-nine, a statement of the approximate proportion of the time of the department devoted to the service of patrolling the highways of the commonwealth for the purpose of controlling and supervising traffic. Said statement shall be the basis for a recommendation by the governor as to the proportion of the appropriations made for expenses of said department which it appears may fairly be charged to the Highway Fund.