In 1974 the speed limit on highways in the United States was reduced to 55 miles per hour in order to save fuel. In t...

Mehran August 15, 2013

The conclusion of this argument is "it follows that the 1974 reduction in the speed limit saved many lives." The author supports this conclusion by noting the drop in fatalities (both in the first 12 months and for the next 10 years) after the 1974 speed limit reduction to 55 mph. This argument is flawed because a temporal sequence does not necessarily imply a causal relationship. This flaw is commonly know as ergo propter hoc (i.e. "after this, therefore because of this").

Nevertheless, the question stem asks us to strengthen this argument.

(A) weakens the argument by pointing out an alternate cause (i.e. people were driving less due to a fuel shortage) to the observed effect (i.e. the decrease in fatalities). We saw less fatalities not because of the 55 mph speed limit but rather because people were driving less.

(D) strengthens the argument by tying driving faster than 55 mph more closely to more fatalities. If there is a higher fatality rate in highway accidents involving motorists driving faster than 55 mph, this would strengthen the author's conclusion that a 55 mph speed limit saved many lives.

Hope this helps! Please let us know if you have any other questions.

Ohemaa January 10, 2019

Can you explain why "E" is incorrect please?

Maybeillgetlucky April 22, 2019

Its giving an alternate explanation

Ravi May 2, 2019

@Ohemaa and @Maybeillgetlucky,

Great questions.

(E) says, "Motorists are more likely to avoid accidents by matching
their speed to that of the surrounding highway traffic than by driving
at faster or slower speeds."

(E) provides us with a method of saving additional lives, but the
problem with (E) is that it doesn't have any effect on the
relationship between slower speeds and fewer fatalities, and that's
the relationship that we're concerned with. As a matter of fact, (E)
actually weakens the argument because if it's true, then the flow of
traffic can move at higher or lower speeds, and the probability of
traffic accidents is dependent upon driving style, not necessarily
slower speed.

Does this make sense? Let us know if you have any other questions!