After May thirty-first, one thousand nine hundred and twenty-six, the cost and expense of maintenance, construction, and improvement of all the highways herein described shall be paid out of moneys appropriated to the State Highway Department for the maintenance, reconstruction, or improvement of State Highways: Provided, however, That routes contained in this act which are now toll roads may be taken over and maintained, constructed, and improved by the State Highway Department at any time prior to May thirty-first, one thousand nine hundred and twenty-six.