LETTERS TO THE EDITORS
Fueling the Debate
To the Editors:
Safety is ignored in "Fuel Efficiency and the Economy" by
Roger Bezdek and Robert Wendling (March–April). CAFE
regulations led to lighter vehicles, thereby increasing injury risk
in traffic crashes (the subject of my own article in American
Scientist, May–June 2003).
Due to physical laws, drivers of lighter cars in single-vehicle
crashes experience higher decelerations, with consequently higher
injury risks. Single-vehicle crashes produce half of driver deaths.
While two-vehicle crashes involve more complex considerations,
reducing the weight of one vehicle generally leads to a small
increase in risk when averaged over both involved drivers.
Nationwide, a lighter fleet kills more people. Details are given in
my 2004 book Traffic Safety. The study cited by Bezdek and
Wendling estimates that CAFE regulations increased annual deaths by 2,000.
By reducing driving costs, CAFE encourages more travel, less
carpooling, and less use of alternative transportation. The average
distance traveled by a vehicle in a year remained essentially
constant at 10,000 miles between the end of World War II and the mid
1970s. Since CAFE started, it has increased to over 12,000 miles.
Since CAFE started, the nation’s fuel use, and the percent of
fuel that is imported, have both increased.
Bloomfield Hills, Michigan
Drs. Bezdek and Wendling respond:
Significant fuel-efficiency improvements will require major changes
in vehicle design, and safety is always an issue when vehicles are
redesigned. However, the relation between fuel economy and highway
safety is complex, poorly understood and difficult to measure.
Improving vehicle fuel efficiency could be marginally harmful,
beneficial, or have no impact on highway safety.
First, few of the technologies identified in our article require
significant vehicle weight reductions, and to the extent that
consumers value power and weight, manufacturers are reluctant to
reduce either to improve fuel efficiency.
Second, it is the relative weight of vehicles rather than their
absolute weight that leads to the adverse risk consequence for the
occupants of the lighter vehicle, and there is evidence that
proportionately reducing the mass of all vehicles would benefit
safety in collisions.
Third, it is important to account for confounding factors and avoid
drawing conclusions from spurious correlations. Because the driver
is a far more important determinant of crash occurrences than the
vehicle, even small confounding effects can lead to erroneous
results. In his 1991 book Traffic Safety and the Driver,
Dr. Evans indicates that the driver is one of the major factors in
94 percent of U.S. traffic crashes, the road environment in 34
percent of crashes, and vehicles in 12 percent. Moreover, younger
drivers tend to drive smaller cars, smaller cars are more common in
urban areas, older drivers are more likely to be killed in crashes
of the same severity and so on. It is difficult to isolate the
effects all of these factors and, in the case of vehicle weight and
safety, adequate measures do not exist to isolate the effects of
Dr. Evans is correct in stating that enhanced CAFE standards, by
reducing the costs of driving, may encourage more travel. However,
empirical studies have found that this effect is minor compared to the
overall fuel savings from CAFE. That said, virtually all analysts agree
that vehicle fuel efficiency standards are a "second best"
alternative, and that substantially increasing gasoline taxes is the
preferred policy. Unfortunately, such increased gasoline taxes are a
political nonstarter in the U.S.