When a bridge or viaduct is built by a municipality and does not cross any place over which the county is authorized to construct a bridge but crosses merely railroad or railroads and private property, the commissioners of counties of the second class A may contract to pay an amount of money, not exceeding thirty per centum of the entire cost of the proposed bridge or viaduct. The bridge or viaduct shall thereafter be maintained as a municipal structure, and the county shall not be liable for any part of the cost of maintenance or repair thereof.
16 P.S. § 2653.1