Cost of street extension assessed as benefits; assessments for parkways.

The United States shall not bear any part of the cost of the acquisition of land for street extensions, but when the condemnation of any land for such purposes is authorized by law the total cost of the land and the expenses of the condemnation proceedings shall be assessed as benefits; in any case where land is condemned for a parkway, including a street or streets, where such parkway is of considerable length with relation to its width, not less than one-half of the cost of the land including the same fraction of the expenses of the condemnation proceedings shall be assessed as benefits; and in any case where land is condemned for a public park, not less than one-third of the cost of the land including the same fraction of the expenses of the condemnation proceedings shall be assessed as benefits.