Vehicle Weight and Automotive Fatalities

Being hit by a 1,000-pound heavier vehicle results in roughly a one in one thousand increase in fatality risk.

Over the past 35 years, the average weight of light vehicles sold in the United States has fluctuated substantially. From 1975 to 1980, average weight dropped almost 1,000 pounds (from 4,060 pounds to 3,228 pounds), likely in response to rising gasoline prices and the passage of the Corporate Average Fuel Efficiency (CAFE) standard. As gasoline prices fell in the late 1980s, however, average vehicle weight began to rise, and by 2005 it had again reached its 1975 levels. In 2008, the average car on the road was roughly 530 pounds -- that is 20 percent -- heavier than the average car on the road twenty years earlier. Heavier vehicles are safer for their own occupants but are more hazardous for the occupants of other vehicles.

In Pounds that Kill: The External Costs of Vehicle Weight (NBER Working Paper No. 17170), authors Michael Anderson and Maximilian Auffhammer study data on all automobile collisions reported to the police in eight states -- a total of 4.8 million collisions. The probability of a fatality, conditional on a collision, is 0.19 percent -- or about one in five hundred. The authors find that being hit by a 1,000-pound heavier vehicle results in a 47 percent increase in the baseline probability of being killed in the accident -- roughly a one in one thousand increase in fatality risk, conditional on a collision. The fatality risk is even higher if the striking vehicle is a light truck (SUV, pickup truck, or minivan). These researchers estimate that the total external costs of vehicle weight that arise from fatalities alone are $93 billion per year. They estimate that the value of the external risk that is generated by the gain in fleet weight since 1989 is approximately 27 cents per gallon of gasoline and that the total fatality externality of heavier vehicles is roughly $1.08 per gallon.

The authors note that traffic accidents are the leading cause of death for persons under the age of 40 and are a major source of life-years lost. Even though lung cancer kills approximately four times as many Americans each year as traffic accidents, because the average lung cancer decedent is 71 years old while the average traffic accident decedent is only 39 years old, the number of life-years lost to traffic accidents is similar in magnitude to the number of life-years lost to lung cancer. This underscores the importance of understanding the determinants of fatal automobile accidents.

--Lester Picker