Where any county or township is responsible for the construction or maintenance of any bridge on a State highway route carrying vehicular traffic over a stream or mill race, or over a stream or mill race and the facilities of any public service company, or on a continuation of a State highway route through any borough or incorporated town, or which is located on a continuation of a State highway route and part of which extends into the municipal limits of a third class city, the responsibility of such county or township shall be assumed by the Commonwealth, except as hereinafter provided. All such bridges shall be taken over by the department and shall be built, rebuilt, repaired, maintained, and may be lighted by the department at the expense of the Commonwealth. The assumption and taking over of any such bridge by the Commonwealth shall not be construed to relieve any person, firm, association, or corporation from any obligation for the construction or maintenance of such bridge under any agreement or order of court or under any order of the Public Utility Commission heretofore or hereafter made.

This section shall not be construed to place upon the Commonwealth the responsibility for the construction or maintenance of any bridge on a State highway route within the limits of any third-class city, if such highway was established subsequently to the first day of January, one thousand nine hundred thirty-one or any bridge which the county, prior to the first day of September, one thousand nine hundred thirty-five, has, with the approval of the secretary, retained as a county bridge and has, by resolution, agreed to maintain and reconstruct in accordance with the standards of the department.

The department shall not take over any such bridge if an order has been issued or a contract has been entered into for the rebuilding or reconstruction of such bridge, until the rebuilding or reconstruction thereof has been completed.