The highways designated in this act as State Highways shall be taken over by the State Highway Department from the several counties or townships of the State, and when so taken over shall thereafter be constructed, improved, and maintained by the State Highway Department, at the expense of the Commonwealth. Said highways shall be taken over in whole or in part, from time to time, as circumstances and conditions will permit: Provided, That, all township roads, abandoned and condemned turnpikes, or turnpikes that may hereafter be abandoned or which may hereafter be condemned and paid for by the county in which the same may be located, and which form a part of any such highways, shall be taken over by the State Highway Department before the first day of June, one thousand nine hundred and twelve. The State Highway Commissioner shall, before taking over any highway under the provisions of this act, give notice in writing to the proper officers of the county or township in which said highway shall lie of his intention so to do, and of the date when the State Highway Department will assume the maintenance and care thereof. The work of maintenance, repair, and construction of said State Highways shall be commenced and carried on as equally and uniformly in the several counties as conditions will allow: Provided, That any county, township, or borough, or incorporated town which may have in contemplation, or under contract or construction, the improvement of any portion of any highway designated herein as a State Highway, shall, upon notice from the State Highway Commissioner of his intention to take over such highway as herein provided, immediately notify the State Highway Commissioner of their intention to make said improvements; and thereupon the status of such highway shall remain the same as it was previous to the passage of this act; and the county commissioners, or the commissioners or supervisors of the township, or councils of the borough or incorporated town, as the case may be, are authorized to complete the improvements of said highway at the expense of the county or township, or borough or town, as the case may be; or the same may be reconstructed as a State-aid highway as is hereinafter provided for: Provided, That upon the completion of any improvement aforesaid, or at the expiration of a period not exceeding eighteen months after the passage of this act, the said highway shall become a State Highway, as herein provided: And be it further provided, That where an agreement or contract exists between any street railway company, or other firm or corporation, and any county, township, or borough, the terms of which require said street railway company, or other firm or corporation, to maintain any highway which is designated under this act as a State Highway, the said agreement shall remain in force, and the State shall succeed to and take over to itself all the rights of said county, township, or borough existing under said agreement or contract. The said street railway company, or other firm or corporation, shall be bound to carry out all of the requirements, and comply with all the terms and conditions, of said agreement with the State, the same as though the said contract or agreement had been originally made between the State and said street railway company or other firm or corporation.