This study used a heteroscedastic ordered probit model to distinguish the effects of vehicle weight, footprint, and height on the severity of injuries sustained by vehicle occupants while controlling for many occupant, roadway, and other characteristics. Model results suggest that the impact of physical vehicle attributes on crash outcomes depends on the number of vehicles involved and is typically more significant in one-car crashes than in two-car crashes. Although vehicles with larger footprints and shorter vehicles were estimated to reduce the risk of serious injury for their occupants in single-vehicle crashes, they appeared to be less crashworthy in two-vehicle collisions. Heavier vehicles were anticipated to be more crashworthy regardless of crash type. Under evolving U.S. fuel economy standards, moderate changes in the weights, footprints, and heights of light-duty vehicles are estimated to have a relatively small impact on crash severities, whereas other factors, such as seat belt use, driver intoxication, and the presence of roadway curvature and grade, are estimated to influence crash outcomes much more noticeably.