The free transportation of pupils, as required or authorized by this act, or any other act, may be furnished by using either school conveyances, private conveyances, or electric railways, or other common carriers, when the total distance which any pupil must travel by the public highway to or from school, in addition to such transportation, does not exceed one and one-half (1 ½ ) miles, and when stations or other proper shelters are provided for the use of such pupils where needed, and when the highway, road, or traffic conditions are not such that walking constitutes a hazard to the safety of the child, as so certified by the Department of Transportation. The Department of Transportation shall take into account the presence of sidewalks along the highway, but such presence or lack thereof shall not be controlling and the department shall consider all relevant safety factors in making its determination as to whether or not walking constitutes a hazard to pupils. All private motor vehicles employed in transporting pupils for hire shall be adequately covered by public liability insurance in such amount as the board of school directors shall require.