The state highway commissioner is further authorized to maintain and improve trunk lines or other highways traversing or upon state parks or other state property, and the connecting trunk lines with the above highways in the same manner as state trunk line highways are required by law to be maintained and improved: Provided, That no such trunk line highways or other highways be laid out and constructed, maintained and improved on any property owned by the Michigan state board of agriculture or the regents of the university of Michigan, unless the Michigan state board of agriculture or the regents of the university of Michigan, as the case may be, by resolution approved by 2/3 of its members respectively gives consent to that effect.