In the past, when there was no highway speed limit, the highway accide

Question

In the past, when there was no highway speed limit, the highway accident rate increased yearly, peaking a decade ago. At that time, the speed limit on highways was set at 90 kilometers per hour (kph) (55 miles per hour). Every year since the introduction of the highway speed limit, the highway accident rate has been at least 15 percent lower than that of its peak rate. Thus, setting the highway speed limit at 90 kph (55 mph) has reduced the highway accident rate by at least 15 percent.

Which one of the following, if true, most seriously weakens the argument?

Which one of the following, if true, most seriously weakens the argument?

(A) In the years prior to the introduction of the highway speed limit, many cars could go faster than 90 kph (55 mph).

(B) Ten years ago, at least 95 percent of all automobile accidents in the area occurred on roads with a speed limit of under 80 kph (50 mph).

(C) Although the speed limit on many highways is officially set at 90 kph (55 mph), most people typically drive faster than the speed limit.

(D) Thanks to changes in automobile design in the past ten years, drivers are better able to maintain control of their cars in dangerous situations.

(E) It was not until shortly after the introduction of the highway speed limit that most cars were equipped with features such as seat belts and airbags designed to prevent harm to passengers.

Bunuel · Accepted Answer

EXPLANATION FROM Fox LSAT

Correlation does not prove causation. Just because a new speed limit and a reduced accident rate happened around the same time does  not  prove that one thing caused the other.  What if something else caused the reduced accident rate? What about the Martians? What if Martian crossing guards stationed themselves every quarter mile along the highway, reminding drivers to drive safely, and that is what caused the reduced accident rate?

Of course the correct answer isn’t going to be about Martians  per se . But if you substitute “some other cause” for “Martians” you’ll get my point. If we can prove that anything else other than the speed limit caused the decline in accidents (less traffic, perhaps? better policing? safer cars?), then we have seriously weakened the idea that the speed limit caused the decline in accidents.

We’re asked to weaken the argument, and my prediction is, “What if the Martians are responsible?”

A) I can only see how this would strengthen the argument, in the sense that it defends the argument against an attack along the lines of “cars can’t even go as fast as the speed limit, so the speed limit is irrelevant.” We’re looking for a weakener.

B) Tricky, but irrelevant. True, most accidents occur on the residential streets around your house, which have low speed limits. But the argument was solely about highway accidents, not all accidents. So this answer could be fact without weakening the argument.

C) This can be true and a lower speed limit could still be safer. For example, I personally always set my cruise control at nine miles per hour over whatever the posted limit is, because I figure a cop won’t want to write a ticket for someone going single digits over the speed limit. So technically, I never obey the speed limit, but they do affect my speed—I drive slower in a 55-mph zone than I do in a 70-mph zone.

D) Yep. This isn’t literally the Martians, but it is the Martians, metaphorically. If this answer is true, then something else is at least partially responsible for the decline in the accident rate. Which makes the argument’s conclusion look pretty silly.

E) Another tricky but irrelevant answer. This answer would explain a decline in  injuries , but wouldn’t explain a decline in  accidents .

Our answer is D.

Nidzo · Answer

(A) Irrelevant and does not provide information. Why has the accident rate dropped? Do the newer cars not go faster than 90 kph?  Incorrect

(B) The passage looks at highways not general roads in the area. The cause for the accidents on the general roads may well be due to other reasons.  Incorrect 
 
(C) Irrelevant. While people may be driving over the speed limit, they could well be driving slower than people were on average a decade ago. Not enough information is provided for this to be relevant or weaken or strengthen the argument.  Incorrect

(D) This weakens the argument. It may well be that the changes in design are what's responsible for the decline in the accident rate. That even if the speed limit had not been implemented that the accident rate would still have declined.  Correct

(E) Irrelevant. The passage is not concerned with the harm of the passengers during an accident, rather the rate of occurrence.  Incorrect

Answer D

Sumi1010 · Answer

The argument concludes -
 Setting the speed limit on highways was set at 90 kilometers per hour --  caused  -- A reduction in the highway accident rate by at least 15 percent.

Prethink -  
To weaken a causal relationship, we have the classical approaches 
- Alternate causation : some other factor reduced the accident rate.
- Reverse causation : The reduction in the rate was the trigger for setting the speed limit. 
- Correlation : Setting speed limit was mere correlated to the reduction in the accident rate.

Let's look at the choices

(A) In the years prior to the introduction of the highway speed limit, many cars could go faster than 90 kph (55 mph).
 This choice gives a reason why the accident rate was higher prior to the introduction of the highway speed limit. 
This statement does not weaken (but supports) the argument. 
(B) Ten years ago, at least  95 percent of all automobile accidents  in the area occurred on roads with a speed limit of under 80 kph (50 mph).
 We may believe that - since at least 95% of automobile accidents occurred when the speed limit of under 80kph, introducing the speed limit of 90kph did not do much to reduce the accident rate. This information weakens the argument.
However, read it closely now. See the traps!

1. ALL automobile accidents = automobile accidents on roads, highways,and stands etc due to high speed, problems in machines, bad weather etc 
Clearly, the argument is limited to automobile accidents at HIGHWAYS ONLY and not on roads.
2. Automobile accidents occurred on roads with a speed limit of under 80 kph. - Does it mean that the most automobiles were actually driving below 80Kph? No.
Irrespective of what speed limit could be, we are concerned with the actual speed of the most automobiles prior to the limit set on highways.

(C) Although the speed limit on many highways is officially set at 90 kph (55 mph),  most  people typically drive faster than the speed limit.
 Most = greater than 50%. 
Still for the remaining 0-50% people, the speed limit matters!. Thus, we can't deny the role of speed limit on accident reduction.  
(D) Thanks to changes in automobile design in the past ten years, drivers are better able to maintain control of their cars in dangerous situations.
 This choice gives an alternate reason to the causal conclusion . Thus, weakens the argument. 
(E) It was not until shortly after the introduction of the highway speed limit that most cars were equipped with features such as seat belts and airbags designed  to prevent harm  to passengers.

It really does not matter what steps are taken for "post accident safety". The information does not impacts the argument.

IMO  D

sivatx2 · Answer

Accident rate, with no speed limit, was at peak 10 years ago, after increasing yearly.
10 year ago, the speed limit was set to 55mph. 
Every year in the last 10, has accident rate at least 15% less than it was at peak.
=> Highway speed limit reduced accident by at least 15%.

(A) In the years prior to the introduction of the highway speed limit, many cars could go faster than 90 kph (55 mph). 
 The argument is about accident rate and speed limit, and hence cars that are faster, are irrelevant to the argument. Eliminate

(B) Ten years ago, at least 95 percent of all automobile accidents in the area occurred on roads with a speed limit of under 80 kph (50 mph). 
 Fact about roads is generic and irrelevant, as the scope of the argument is limited to "highways". Eliminate

(C) Although the speed limit on many highways is officially set at 90 kph (55 mph), most people typically drive faster than the speed limit. 
 People driving faster(violating speed limit) may or may not impact, but it is irrelevant to the argument on accident rate and speed limit. Eliminate

(D) Thanks to changes in automobile design in the past ten years, drivers are better able to maintain control of their cars in dangerous situations. 
 This change happened since the speed limit was enforced and can be the real cause in the reduction of accident rates. It clearly states it happened in the last 10 years. So this is the best answer choice. Keep

(E) It was not until shortly after the introduction of the highway speed limit that most cars were equipped with features such as seat belts and airbags designed to prevent harm to passengers. 
 Accident is different from 'harm to passengers'. There maybe accident that happens without harm to passengers. Eliminate.

So, D is the best answer choice.

unraveled · Answer

In the past, when there was no highway speed limit, the highway accident rate increased yearly, peaking a decade ago. At that time, the speed limit on highways was set at 90 kilometers per hour (kph) (55 miles per hour). Every year since the introduction of the highway speed limit, the highway accident rate has been at least 15 percent lower than that of its peak rate. Thus, setting the highway speed limit at 90 kph (55 mph) has reduced the highway accident rate by at least 15 percent.

Which one of the following, if true, most seriously weakens the argument?

Which one of the following, if true, most seriously weakens the argument?

(A) In the  years prior to the introduction of the highway speed limit , many cars could go faster than 90 kph (55 mph). - WRONG. The very tenet of the passage is not considered instead it is shifted. The scope shift is what kills this one.

(B) Ten years ago, at least 95 percent of all automobile  accidents in the area occurred on roads with a speed limit of under 80 kph  (50 mph). - WRONG. 2nd best and a trap that is subtle to see. When we are talking about highway accident rate with speed limits of 90kmph, ones with 80kmph limit makes no sense. So, we have a scope shift which is an essential part to consider while answering the question.

(C) Although the speed limit on many highways is officially set at 90 kph (55 mph),  most people typically drive faster than the speed limit . - WRONG. What about accident rates because of this is unknown. So, eliminate.

(D) Thanks to  changes in automobile design in the past ten years, drivers are better able to maintain control  of their cars in dangerous situations. - CORRECT. We have another factor that is responsible for such decrease.

(E) It was not until shortly after the introduction of the highway speed limit that  most cars were equipped with features such as seat belts and airbags designed to prevent harm to passengers.  - WRONG. Did those features let accident rate fall or increase. We are not sure.

It was between B and D but B lacks a crucial point as discussed above.

Answer D.

agrasan · Answer

Hi experts  KarishmaB   MartyMurray   DmitryFarber

(B) Ten years ago, at least 95 percent of all automobile accidents in the area occurred on roads with a speed limit of under 80 kph (50 mph).

Can we also reject (B) on the basis of reasoning that  "percent of automobile accidents"  is a different metric from  "accident rate" ? The argument's conclusion is about "accident rate" only, thus, (B) becomes irrelevant for us.

ParamjitDasGMAT · Answer

Not quite, the reason B is irrelevant is that the argument is about the accident rate on *highways*, not ALL accidents.

Otherwise, the percentage of automobile accidents and accident rates, in this context, would be quite similar.

Hope this helps.

agrasan · Answer

Thanks, actually, I didn't understand how they would be similar.
 Percent of automobile accidents  should be automobile accidents attributed to something out of all automobile accidents whereas  accident rate  should be number of accidents out of total trips/journeys.

guddo · Answer

In the past, when there was no highway speed limit, the highway accident rate increased yearly, peaking a decade ago. At that time, the speed limit on highways was set at 90 kilometers per hour (kph) (55 miles per hour). Every year since the introduction of the highway speed limit, the highway accident rate has been at least 15 percent lower than that of its peak rate. Thus, setting the highway speed limit at 90 kph (55 mph) has reduced the highway accident rate by at least 15 percent.

Which one of the following, if true, most seriously weakens the argument?

Which one of the following, if true, most seriously weakens the argument?

Accidents on highways were highest ten years ago. A 90 kph speed limit was introduced then, and since then the highway accident rate has been at least 15% below that peak. The argument concludes the speed limit caused at least a 15% reduction.

(A) In the years prior to the introduction of the highway speed limit, many cars could go faster than 90 kph.

This does not weaken. The argument is not about what cars are capable of, but about what caused the later drop in accidents.

(B) Ten years ago, at least 95% of all automobile accidents occurred on roads with a speed limit under 80 kph.

This is about all roads, not specifically highways. The argument is about the highway accident rate, so this does not directly explain why that highway rate fell after the limit.

(C) Most people typically drive faster than the speed limit.

This weakens somewhat, but it is not decisive. People can exceed 90 kph and still be driving slower than they used to when there was no limit, so this does not clearly remove the speed limit as a cause.

(D) Thanks to changes in automobile design in the past ten years, drivers are better able to maintain control in dangerous situations.

This is a strong alternative cause: improved vehicle control could reduce the  accident rate  regardless of any speed limit. So the drop could be due to safer cars, not the 90 kph rule.  This most seriously weakens the causal claim.

(E) Most cars were equipped with seat belts and airbags only shortly after the limit was introduced.

Seat belts and airbags mainly reduce injury severity, not the number of accidents, so this is a weaker alternative explanation for a lower accident rate.

Answer: (D)

MartyMurray · Answer

You are correct about the two metrics being different ones. At the same time, we have to be careful about eliminating a choice simply because it presents a different metric, because that metric could be relevant.

For example, if the conclusion were that the speed limit had caused a reduction in the overall accident rate, not just the highway accident rate, then the fact that most accidents occur off highways could weaken the case for the conclusion by indicating that a 15-percent reduction in the highway accident rate does not constitute a 15-percent reduction in the overall rate.

So, in general, we have to be careful not to eliminate choices merely because they bring up new variables. We have to instead consider holistically whether information about a particular variable materially affects what we know about a situation in a way such that the strength of the argument is affected.

shanalshekhar · Answer

Why is C wrong? If most people are driving at speeds > 90 and accidents have still gone down, then speed limit never played a role. How and why should I read more into this? I see other explanations on this, and they just seem too forced as if trying desperately to show why D over C

guddo · Answer

(C) is wrong because it does not show that the speed limit had no effect. “Most people drive faster than the limit” can still be true even if the limit reduced speeds.

Here is the key logic: the argument needs a cause for the 15% drop. (C) only says many people exceed 90, but it says nothing about whether they used to drive even faster when there was  no  limit, or whether enforcement and signage still lowered average speeds. So the speed limit could still have reduced the accident rate even if most drivers go, say, 95.

(D) is stronger because it gives a clear  independent alternative cause  that could lower accidents even if speeds did not change. That directly breaks the “thus, the speed limit caused it” link.

MartyMurray · Answer

(C) is tricky, but we can eliminate it for three reasons.

One is that " most people typically drive faster than the speed limit" means that other people drive under the speed limit. So, even if most people exceed the limit, the limit could be slowing down enough people to make a difference.

The second is that, even if "most people typically drive faster than the speed limit," the presence of the speed limit could still be affecting how people drive. We all see that result in the real world. Many people exceed the speed limit but drive less fast than they would without it. We can use common knowledge in answering Critical Reasoning questions, and common knowledge of the effects of speed limits in the real world can be used here.

Finally, (D) is a much stronger answer, and this is key because this is an LSAT question, and LSAT questions are sometimes different from GMAT questions in the following way. Whereas GMAT questions usually have just one answer choice that works at all, LSAT questions sometimes have multiple answer choices that arguably work at least somewhat, and we have to choose the one that works the best.

So, even if we were to decide that (C) casts a little doubt on the conclusion, knowing that this is an LSAT question, we could safely choose the much stronger choice (D).

vasu1104 · Answer

in past, no speed limit - highway accident rate increased yearly and peaked decade ago. 
 speed limit was set at 90 kph, highway accident rate has been at least 15% lower than that of its peak rate. 
 conclusion- speed limit has reduced accident rate by at least 15%.

so since the time they introduced the speed limit, accident rate dropped to certain rate so they made conclusion that speed limit was the reason for such drop in rate. no other reason was there. here we are seeing causation and correlation relationship.

A but we know in the past no limit was there, so this already is mentioned in passage, out. 
 B passage is only concerned with highway accident rate and not all accident rate, out. 
 C no impact and irrelevant. out. 
 D if that is the thing then they are now in more control on how to handle the dangerous situation and can aviod being caught in accident. so its not speed limit but new design of cars that helped them to avoid accident. keep. 
 E this talks about preventing harm but thats not we are concerned here, reject. also despite preventing harm accident can still happen. out.

In the past, when there was no highway speed limit, the highway accide

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In the past, when there was no highway speed limit, the highway accide

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