A Medical College of Wisconsin study found small-overlap collisions result in increased head, chest, spine, hip, and pelvis injuries. This sort of collision is common on two-lane roads with two-way traffic where a center median is absent. Single vehicle crashes (into a tree or a pole) account for 40 percent of small-overlap crashes. According to the IIHS, 25% of frontal crash deaths are due to small overlap crashes, with the outer front wheel first to receive the impact forces rather than the more central crash absorbing structure.