PrepTest 129, Section 2, Question 20
In the past, when there was no highway(81 more words not shown)
Which one of the following,(7 more words not shown)
- AIn the years(19 more words not shown)
- BTen years ago,(24 more words not shown)
- CAlthough the speed(21 more words not shown)
- DThanks to changes(21 more words not shown)
- EIt was not(29 more words not shown)
Reading the argument
The accident rate fell after the speed limit was introduced. That timing makes the speed limit a plausible explanation, but does it establish that the limit itself reduced the accident rate by at least 15 percent?
What else changed during those ten years? Perhaps driver training improved, or cars became easier to control in dangerous situations. A technology that helps a driver avoid hitting another car could reduce accidents even if the speed limit stayed the same.
We need to keep the outcome precise. The claim is about the accident rate, not how badly people are hurt once an accident occurs. Better hospital care might reduce deaths without preventing any crashes. Likewise, fewer crashes in total would not automatically establish a lower rate without knowing how much driving occurred.
What we’re looking for
The weakening question calls for an alternative explanation of the reduced accident rate. The speed limit might still contribute, but evidence of another contributor would make it harder to attribute a reduction of at least 15 percent in the accident rate to that one change.
Working the answers
- A
Cars' ability to exceed the later limit does not challenge its effect. It is consistent with a limit reducing how fast people drive. A says nothing about another reason accidents declined or why imposing the limit would fail to help.
- B
This gives the distribution of all accidents across roads ten years ago. The argument concerns a change in the accident rate on highways. Even if highways accounted for only a small share of all accidents, their own accident rate could fall by 15 percent. A percentage of all accidents and a percentage reduction within one category answer different questions.
- C
Driving above the limit does not mean the limit had no effect on speed. Suppose drivers formerly went 90 miles per hour and now go 65 despite a 55-mile-per-hour limit. They are still speeding, but they have slowed down substantially. C never compares their current speeds with their earlier speeds, so it does not show that the policy failed to reduce accidents.
- DCorrect
Better control gives drivers another way to avoid crashes. A driver who once would have lost control might now steer safely through the same dangerous situation because the car's design improved.
That provides a competing explanation for at least some of the decline. The speed limit could still have helped, but the observed drop alone would no longer justify crediting it with a reduction of at least 15 percent. Some of the reduction might instead come from the design changes.
- E
Seat belts and airbags are described here as preventing harm to passengers. That can change the consequences of a crash without changing whether the crash happens. A minor collision and a fatal collision both count as accidents. E would matter to a claim about injuries or deaths, but it does not supply the accident-prevention mechanism D supplies.
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