The heavy and light commercial vehicles are equipped with protection devices to enhance the safety of occupants in small vehicles in the event of under run and to reduce the degree of intrusions. These protection devices are SUPD (side under run protection devices), RUPD (rear under run protection devices), FUPD (front under run protection devices). Any passenger vehicles can impact with the heavy vehicles either from rear, front or side and meet the sever accident. During these types of impacts, there is a possibility that the passenger vehicle will go under the front, rear or side part of the truck and bus and cause serious injuries to the occupants. Side underrun protection device is one of the important system implemented in Vehicles as a regulatory requirement (as per IS 14682: 1999) for passive safety of N2 and N3 category vehicles. This device gives protection for small vehicles (N1 and M1 category) against under running of big vehicles (N2 and N3 category) in the event of side collision. This work describes the study of various crossection of Side Underrun protection bars during the design process to achive the best feasible design. The New SUPD bar crosssection was designed without changing the vehicle mountings to meet the acceptance criteria during the side collision with a good weight and cost reduction. The motivation behind this work is to remove the additional reinforcement brackets used for SUPD bar mountings and implement the optimized design. The challenges faced in this work is to maintain the SUPD assembly strength as reuired to meet the requlatory requirement. In order to reduce the design cycle and to validate the new design finite element method is used using LS-Dyna and Nastran.with this new study a good weight reduction is achieved while meet all the design criteria.