Section 56. A street railway constructed upon private land shall not be opened for public use until the department, after examination, certifies that all laws relative to its construction and all requirements of the department have been complied with, and that it appears to be in a safe condition for operation. The department may, at any time after the opening of a street railway for public use, order such changes and improvements to be made in the construction and operation of any part thereof upon private land as it deems necessary for public safety in the use thereof; and such order shall be complied with by such company.