Blunt carotid artery injuries are commonly characterized by intimal failures leading to vessel dissection, resulting in cerebral infarction and ischemic stroke. These injuries typically occur in motor vehicle collisions and, although the incidence is low, are associated with high morbidity and mortality rates. Previous studies of arterial failure mechanics did not quantify intimal failure. The present study quantified intimal failure mechanics relative to catastrophic vessel failure in human and porcine arteries. Under mechanical distraction, human internal and common carotid arteries demonstrated similar behavior, with only ultimate stress being significantly different (p<0.05). Porcine aortas sustained significantly greater stress and strain at initial intimal failure, strain at ultimate failure, and intimal-to-ultimate stress and strain ratios. Human carotid arteries were obtained from cadavers of advanced age that were frozen prior to excision. Because these factors may alter soft-tissue mechanical response, young, fresh porcine aortas are likely a better model of blunt carotid artery injury. This study provides a mechanical basis for clinical findings of intimal failure in blunt carotid artery injury.