The several cities of this commonwealth are hereby authorized to locate and build viaducts or bridges, to be used as public highways, over rivers, creeks, streams, railroads and private property, or over and across any of them, whether the said viaducts or bridges be wholly within, or partly without and partly within, the city limits, for the purpose of uniting two or more different streets or highways, or separate parts of the same highway or extension thereof.
53 P.S. § 2501