Bulletin #2336, Maine Farm Safety Program: Roll-Over Protective Structures and Power Takeoff Shields (PDF) By Dawna L. Cyr, Farm Safety Project Assistant, and Steven B. Johnson, Ph.D., Extension Crops Specialist For information about UMaine Extension programs and resources, visit extension.umaine.edu.Find more of our publications and books at extension.umaine.edu/publications/. Two major safety features on tractors are