Power to construct or maintain public b ridges.-

The Commissioner when authorized by the Corporation in this behalf may agree(a) with any person to adopt and maintain any existing or proposed bridge, Viaduct or archand approaches as part of a public street, or as property vested in the Corporation; or (b) for the construction or alteration of any such bridge, viaduct or arch or for the purchase or acquisition of any adjoining land required for the foundation and support thereof, or for the approaches thereto, either entirely at the expenses of such person or partly at the expense of the Corporation.