The board of supervisors of any county may expend any portion of the amounts thus received by that county in the construction, maintenance, improvement or repair of streets, bridges, and culverts within those cities in the county the governing bodies of which by ordinance or resolution authorize such work of acquisition of any real property or interest therein, or rights-of-way, construction, maintenance, improvement or repair. For this purpose each board of supervisors shall provide by ordinance the basis and conditions upon which allocations will be made from its road fund for expenditure upon streets, bridges, and culverts in cities within the county.