PT38.S4.Q14 - reducing speed limits

babybenny

http://7sage.com/lsat_explanations/lsat-38-section-4-question-14/

I have questions about (B) and (D)

First of all, an answer choice like (B), "ignore the possibility of benefits from lowering speed limits "other than" environmental and safety benefits.
I can see sometimes it's a right answer because a flaw is an author doesn't consider other factors except for the factors mentioned in a stimulus. But sometimes it's a wrong answer because it's out of scope just like Q.14.
So I can't really find out what kind of stimulus should be if an answer choice like (B) is a right answer.
Whenever I encounter an answer choice like (B), I'm always stuck.

Lastly, about (D), how is it still a right answer? Shouldn't it say both saving lives and protecting the environment just like the author says?
I mean it only says about "protecting the environment" and doesn't say about "saving lives". So that's why I entirely don't understand why D is an answer.

Can anyone explain me?
Thanks!

sicsemper

First off I think this is a good case of needing to be really specific about what exactly the stimulus is arguing. There are a lot of questions/answer choices that set you up for failure by exploiting loose phrasings of the argument - and that's what's going on with B.The argument is designed only to show that reducing speed limits does not protect lives or the environment, so considering any benefits other than protecting lives or the environment would not impact the conclusion about those two things (why B is not the correct answer). Now, if the conclusion of the argument was that reducing speed limits is "not worthwhile" or "more trouble than they're worth" (or another, broader, claim than the one the stimulus makes) then B would be more attractive, as there might be other evidence outside of environmental benefits or safety benefits that undercut the argument that reducing speed limits is "not worthwhile".

On D - this is one correct answer. I think you're right that it only addresses the flawed connection between one of the premises and the conclusion. This could just as easily say that it "fails to consider that collisions would be less dangerous at lower speeds", which I think would also be correct. But that it only addresses one of the premises doesn't make it incorrect I think, especially since there's no better answer.

vandyzach

Sicspmer, that was a wonderful explanation! Could you answer a question about answer choice (D)?

I don't think (D) is logically correct. What do you think? Here is what I thought during my PT and also during my review:

The argument doesn’t assume that total emissions are determined PRIMARILY by the amount of time the trip takes- it just assumes that the total emissions for a car trip is determined more by time on the road than it is by driving speed. The primary determinant could be like engine size or something, and as long as the total emissions is determined more by time on the road than by driving speed, the argument could still work, so this is barely not the flaw.

Since I eliminated (D), I chose (A) because it seemed the argument jumped from "speed limits" to "driving speed", and I figured it was the closest thing to a right answer.

sicsemper

Gotcha. I think we have different readings on the relationship between speed and time on the road. I don't think it's the case of one versus the other but rather that there's a pretty high correlation between the two and one leads to the other: slower speed limit must mean more time on the road. Which, the argument claims, means more emissions. But it's possible - even likely - that slower speed limits would yield lower emissions per time unit of travel to compensate for any increase in total emissions from an increase in time on the road such that total emissions would be lower with a lower speed limit. That's what the argument ignores - that there's another variable that impacts total emissions to a greater degree than does the total amount of time on the road.

vandyzach

Oh my gosh- how could I have not made that connection between speed and driving time?! Thanks so much for your explanations, Sic- you identified my problem perfectly!

This flaw is now so easy to spot!

sicsemper

No prob