In car/truck collisions, the size, weight, and stiffness mismatch results in much larger structural deformation of the car re to the truck. This is further aggravated when the passenger vehicle trends beneath the rear or side of the taller truck. Truck under-ride increases the probability of death or serious injury for smaller vehicle occupants due to intrusion of arts of both small car and the truck into the smaller car passenger compartment. A computational technique is utilized in this study to quantify the influence of a side guard attached to a large truck in reducing the intrusion to the car and thus reducing the injury stained by the occupants of a car in side impact scenarios. A parametric study is utilized to identify the critical guard eight resulting in optimum cabin deceleration and compartment intrusion of the small car.