On or before January 1 of each year, the commissioner shall notify all cities, towns and unincorporated places of the amounts of aid being allotted in each fiscal year. Payments shall be made as follows: 30 percent in July; 30 percent in October; 20 percent in January; and 20 percent in April. These funds shall be used only for highway construction, reconstruction or maintenance purposes. Whenever any city, town or unincorporated place is unable to utilize the full amount of this apportionment for highway construction, reconstruction or maintenance purposes in any given municipal fiscal year, the unused balance may be carried over to the following municipal fiscal year and expended for highway construction, reconstruction or maintenance purposes.