Self-study
A government study indicates that Support raising speed limits to reflect the actual average speeds of traffic on level, straight stretches of high-speed roadways reduces the accident rate. █████ ███ ██████ ███████ █████ ███ ██████ ████████ █████████ ██ ██████████ ████████ █████ ██ ██ ███ ██████████ ███ ████ ███ █████ ███ ██████ ████ ██████ ██ ███ ██ █ ███████ ████████ █████ █████ ███ ██████ ████████ █████████ ██ ███ ████ █████████
Objective: Find the Principle
The author claims that all level and straight highways should have their speed limit changed to 120 kph. This is because the proposed new speed limit would better match the actual speed at which people drive on those highways. And what's more, a study has shown that changing speed limits on those kinds of roads to reflect actual driving speeds reduces the accident rate.
We need to find a principle that acts as a premise-to-conclusion bridge, which means we need to find the gap that needs bridging in the first place. The author's reasoning seems solid: changing speed limits will reduce accident rates, so we should change the speed limits. But what's missing is the actual value judgment, that we should do things that reduce accident rates. The author doesn't explicitly state this principle, so by finding it in the answer choices, we can bridge from the factual premises to the value-judgment conclusion.
Keep in mind, the exact wording of the principle isn't important, as long as it effectively bridges the gap! This same idea could be expressed in many ways. It could use formal, conditional language (if a measure would reduce the accident rate, then it should be implemented), could be very specific (any change to a speed limit for defined sections of road that would improve traffic safety...), or could be very general (any effective public safety measure...). All of these possibilities would do just as good of a job at bridging the gap, so we need to pay attention to the effect of the principle rather than its exact phrasing.
21.
Which one of the following ███████████ ██ ██████ ████ █████ ██ ███████ ███ █████████ ██████
a
Uniform national speed ██████ ██████ █████ ████ ██ ██████████ █████████
This leads to a different conclusion than the author's, so can't bridge the gap. We can see this by reformulating (A) into its contrapositive: uniform speed limits should not apply to non-high-speed roadways. Now it's more clear that this doesn't match the argument—the author never claims that a uniform limit shouldn’t apply to low-speed roads, just that it should apply to certain highways.
b
Traffic laws applying ██ ██████████ ████████ ██████ █████ █████████ ██████ ███ ███████
The author is trying to argue for uniform application of a particular speed limit on the basis of saftey, not merely on the basis of uniformity. The uniformity is important only insofar as it has the potential to increase safety. Notice (B) doesn't address safety. According to (B), as long as the speed limit is uniform, i.e., the same everywhere, then it's fine. But uniformity alone isn't enough. Our author specifically wants the speed limit to be at 75 mph. (B) doesn't deliver that. (B) is agnostic about the actual speed limit.
Another way to see the deficiency in (B) is to realize that the author isn't arguing for an existing measure to be applied nation-wide, but rather for a new national measure of 75 mph to be implemented.
c
A uniform national █████ █████ ███ ██████████ ████████ ██████ ██ ███ ████ ██ ███ ████ ████████ ████ ███████ █████ ███████ ██████ ██ ████████
This describes a necessary condition for a national speed limit, but that would only be useful in determining that certain roadways should not have a uniform speed limit. Since the author claims that there should be a uniform national speed limit, this principle doesn’t help; it leads to the wrong conclusion.
d
Long-standing laws that ███ ██████ ████████ ███ ████████ ███ ████ █████
This both has the wrong trigger and leads to the wrong conclusion. The author doesn't discuss any long-standing laws (or violation of laws), meaning the facts given don't trigger this principle. Further, the author's conclusion doesn't involve any judgment about what is or isn’t a good law, so this principle can't bridge to the correct conclusion.
e
Any measure that ███████ ███ ████ ██ ███████ █████████ ██████ ██ ████████████
This is the bridge we're looking for. The premises tell us that uniform speed limits (set at 75 mph on level, straight highway stretches) reduce accident rates, so this principle is triggered. Based on the principle, such a measure should be implemented, which matches the author’s conclusion that a uniform limit should be set nationwide. This is a more general bridge than we strictly need, but it does correctly bridge the gap.