PT61.S2.Q21 - Uniform National Speed Limit

benjipants

https://7sage.com/lsat_explanations/lsat-61-section-2-question-21/

I'm trying to understand where my thinking went wrong here, because the truth is that even after spending a lot of time with this question, I know I could make the same mistake on a similar question in the future.

The stimulus says that "A government study indicates that raising speed limits to reflect the actual average speeds of traffic on level, straight stretches of high-speed roadways reduces the accident rate. Since the actual average speed for level, straight stretches of high-speed roadways tends to be 120km/hr (75mph), that should be set as a uniform national speed limit for level, straight stretches of all such roadways."

I'm reading the stimulus with a critical eye, so immediately I'm thinking: "Well, the average speed might tend to be 75mph, but maybe the actual average speed on some stretches in some places of the country is much lower, and in other places much higher. So maybe instituting a "national speed limit" that is uniform across all locations would actually lead to more accidents. What justifies the speed limit being set uniformly? Why not adjust it specifically for each stretch of roadway based on the actual average speed for that location?"

So I read down, looking for an answer choice that speaks to this apparent flaw (as I see it) in the reasoning, an answer choice that tells me why the adopted speed should be uniform. So of course I picked answer choice B. "Traffic laws applying to high-speed roadways should apply uniformly across the nation."

I DO see now that answer choice B leaves out an important element (it doesn't justify why THIS particular law should be adopted), but with my concept of the argument's flaw in mind, I didn't see answer choice E as viable. I got to the answer choice still thinking that the question of whether adopting this traffic law uniformly across the country would in fact reduce the "rate of traffic accidents" was still open to question.

At least answer choice B seemed to address the gap (as I saw it) in the argument.

Where was I off in my thinking?

Rachel Yoon

I also chose B, and here is what I thought.
The argument's conclusion is saying "that should be set as a uniform national speed limit for level, straight stretches of all such roadways."
So, I think the argument narrowed down the scope.

The answer choice B says "should apply uniformly across the nation" and I thought this was too much for our argument since our argument only talked about "such roadways".
So other roadways which have different actual average are not in the right scope, I think. As you mentioned, what if some of them is not on level, or not straight, or have different actual avrg speed? or maybe not even a high-speed roadways..?

Since the question is PSA type, if we have E in our premise,
the argument would go like
p1: raising speed limits to reflect the actual average speeds...reduces the accident rate.
p2: Any measure that reduces the rate of traffic accidents should be implemented.
p3: Since the actual average speed for... 120km/hr(75 miles/hr),
con: that should be set as a uniform national spped limit for level, straight stretches of all such roadways.

which would be valid.

Hope this helps!

Positive

I think, because this is a PSA question, the scope of the conclusion regarding roads is not the main problem with B.

As JY has explained, B talks about traffic laws, and if you look into the premises carefully, they do not mention any traffic law. It just talks about raising speed reduces the accident rate. AND the number just happens to be 120km/h.

Please let me know I'm missing the point here.