If the Commission shall decide that such a crossing should be eliminated or relocated it shall apportion, assess and require the payment by such railroad company of its proper pro rata share of the expense incident to the construction and grading of any highway or road appurtenant to such elimination or relocation but the cost to be assessed against such railroad company shall not exceed its proper pro rata share for more than one fourth of one mile and, in the case of railroads independently operated having less than eighty miles of road within this State, shall not exceed its proper pro rata share for more than one eighth of a mile.