The commissioner is authorized and directed to erect on any class I, class II or interstate highway under his jurisdiction, reflective directional signs designating the route or exit to the nearest general hospital. Such signs shall be erected in those locations as the commissioner, after consultation with the local authorities, may determine to be in the best public interest, provided, the local authority gives adequate assurance to the commissioner that suitable hospital signs will be erected within the local jurisdiction at local expense as a continuation of the hospital directional signs erected hereunder. The cost for the signs and erection of such signs shall be a charge upon the highway fund.