The provisions of Section 56-1-37 shall not apply to industrial or interplant operations and to cabooses or yard engines used in yard movements within switching limits having a one-way route mileage of 25 miles or less. The provisions of this act shall not apply to cabooses or locomotives presently operated by railroads having less than 100 miles of main and branch line trackage; provided, however, that any additional cabooses acquired by said railroads shall comply with all of the provisions of this act.