Any balance of appropriations in excess of that required to be distributed to the towns, under the formulas set forth in sections 13a-175a to 13a-175d, inclusive, as of June 30, 1977, and annually thereafter, may be made available by the Governor, upon application of the selectman or other authority having charge of highways in any town, to be used to defray, in whole or part, the cost of repairs, improvements, alteration or replacement of roads, bridges and dams in such town which, in the opinion of the Governor, with the advice of the Commissioner of Transportation, in the case of roads or bridges, and the Commissioner of Energy and Environmental Protection, in the case of dams, constitute a threat to public safety as a result of damage resulting from a natural disaster. On or after June 30, 2018, any such balance shall lapse to the resources of the Special Transportation Fund and shall not be transferred to the General Fund.