Motor vehicle crashes are a major cause of death and injury in the United States. Quantifying the enormous impacts on society resulting from these deaths and injuries has been the subject of numerous studies. This paper discusses the present state of knowledge of an approach to quantifying societal impacts, called impairment, in which the parameter of interest is the time injured persons are unable to function at their pre-injury level. In this approach, a "whole body impairment factor" for each specific injury is multiplied by the life expectancy of the injured person, resulting in "person-years of impairment". The duration of the impairment for less than lifetime, and any reduction in life expectancy as a result of the injury are accounted for in the methodology. Topics of particular emphasis in the paper are the definition of impairment, the attributes that comprise impairment, and comparisons with other concepts that have been developed to quantify health status and the impact of injuries on society.