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.
Leonard Evans
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 weight
alone.
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.
