On any railroad train where the engine is accompanied by a tender of the Vanderbilt or similar type of construction and where the clearance between the overhang of the roof of the cab of the engine and the top of the tender accompanying the engine is less than twenty-eight inches, an opening not less than twenty-four inches square shall be cut out in the overhang of the roof of the cab, for the purpose of enabling an engineman with safety to go from the cab of the engine to the top of the tender.