Older adults are more vulnerable than younger adults: their injuries will be more severe given an identical collision impact. With the same impact force, the fatality rate is approximately three times higher for a 75 year old motor vehicle occupant than for an 18 year old (see also fatality ratio). The physical vulnerability has the severest consequences during 'unprotected' journeys such as walking and cycling. This physical vulnerability is a less important factor for car drivers, but it still has an influence on injury severity. Physical vulnerability is mainly caused by age-related disorders such as osteoporosis.