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705-805 Level|   Logical Flaw|               
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avigutman
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Urban rail systems have been proposed to alleviate traffic congestion 06 Jun 2024, 09:43
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PReciSioN
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­Yes, as you suggest, PReciSioN, the officials CAN argue that 
Quote:
PReciSioN
URS has increased ridership of non-commuters which has decreased traffic congestion (albeit by a small amount.)
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And, if they had argued that, it would indeed be a flaw for them to not have given
Quote:
PReciSioN
any information about the ridership of non-commuters
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But that wasn't their argument... They argued commuting trips in that city represent just 20 percent of urban travel.

When evaluating a response's vulnerabilities to criticisms, one must stick to what that response WAS, not to what that response COULD have been.
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Urban rail systems have been proposed to alleviate traffic congestion 06 Jun 2024, 10:14
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avigutman

PReciSioN

 
­Yes, as you suggest, PReciSioN, the officials CAN argue that 
Quote:
PReciSioN
URS has increased ridership of non-commuters which has decreased traffic congestion (albeit by a small amount.)
And, if they had argued that, it would indeed be a flaw for them to not have given
Quote:
PReciSioN
any information about the ridership of non-commuters
But that wasn't their argument... They argued commuting trips in that city represent just 20 percent of urban travel.

When evaluating a response's vulnerabilities to criticisms, one must stick to what that response WAS, not to what that response COULD have been.
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­Ahh, I see!! avigutman , 

So while stating that commuting trips in the city represent just 20% of urban travel, the officials' logic was "well, commuting trips are just 20% of urban travel, so they probably don't cause much traffic congestion as well" instead of "commuting trips are 20% of urban travel, so even if URS was not effective for them, it was (assumed) effective for non-commuters". 

Although, their logic seems to be quite defensive, instead of actively trying to prove that URS is effective. What's more even if commuting trips represented only 20% of the congestion, I don't quite see how they have countered the original argument, since they are essentially stating nothing about why URS is effective.

Thanks for your help Avi !!
 
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Urban rail systems have been proposed to alleviate traffic congestion 13 Apr 2025, 01:08
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Isn't the given passage a bit ambiguous here, because it says 'commuting trips in that city represent just 20% of urban travel'

urban travel could also be US wide or state wide right? how are we sure it means urban travel of that city itself
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Urban rail systems have been proposed to alleviate traffic congestion 13 Apr 2025, 23:19
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No, there is no ambiguity. From context it is clear that 'urban travel' means 'urban travel in that city.'
When they are evaluating the case of a particular city, the metrics would talk about that city only. GMAT will expect you to understand this logic.

Prakruti_Patil
Isn't the given passage a bit ambiguous here, because it says 'commuting trips in that city represent just 20% of urban travel'

urban travel could also be US wide or state wide right? how are we sure it means urban travel of that city itself
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Urban rail systems have been proposed to alleviate traffic congestion 17 Jul 2025, 08:03
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There is something which I found difficult about the wording of this question - "The response of the officials to claim that urban rail systems are ineffective(?)"
From the passage, we know that urban rail systems were proposed to alleviate traffic congestion, and that they might be ineffective, which we are given an example for.

Then we are told that "some officials who favour urban rail systems have attempted to counter this argument...." - This means that the officials favor the rail system, why would they claim it is ineffective?

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Urban rail systems have been proposed to alleviate traffic congestion, but results in many cities have been cited as evidence that this approach to traffic management is ineffective. For example, a U.S. city that opened three urban rail branches experienced a net decline of 3,100 urban rail commuters during a period when employment increased by 96,000. Officials who favor urban rail systems as a solution to traffic congestion have attempted to counter this argument by noting that commuting trips in that city represent just 20 percent of urban travel.

The response of the officials to the claim that urban rail systems are ineffective is most vulnerable to criticism on the grounds that it

(A) presents no evidence to show that the statistics are incorrect

(B) relies solely on general data about U.S. cities rather than data about the city in question

(C) fails to consider that commuting trips may cause significantly more than 20 percent of the traffic congestion

(D) fails to show that the decline in the number of urban rail commuters in one U.S. city is typical of U.S. cities generally

(E) provides no statistics on the use of urban rail systems by passengers other than commuters

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ID: 500319
CR11080.02­
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Urban rail systems have been proposed to alleviate traffic congestion 29 Jul 2025, 18:29
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kabirgandhi
There is something which I found difficult about the wording of this question - "The response of the officials to claim that urban rail systems are ineffective(?)"

From the passage, we know that urban rail systems were proposed to alleviate traffic congestion, and that they might be ineffective, which we are given an example for.

Then we are told that "some officials who favour urban rail systems have attempted to counter this argument...." - This means that the officials favor the rail system, why would they claim it is ineffective?
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The wording is certainly a bit tricky here.

You're right, we have the officials who favor urban rails systems and the critics who are against urban rail systems. The critics are the ones calling urban rail systems ineffective.

So how would the officials RESPOND to the critics' claim that urban rail systems are ineffective? That's what the question is asking.

I hope that helps a bit!
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Urban rail systems have been proposed to alleviate traffic congestion 15 Sep 2025, 08:44
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C trips=only 20% of urban trips . But 20% of urban trips may be > 20% of congestion.
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Urban rail systems have been proposed to alleviate traffic congestion 15 Sep 2025, 18:37
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Hello bb KarishmaB GMATNinja egmat
I wasnt able to understand the gap/flaw in the officials reasoning. Could someone please explain that?
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Urban rail systems have been proposed to alleviate traffic congestion 15 Sep 2025, 19:10
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Mehakgyl
Hello bb KarishmaB GMATNinja egmat
I wasnt able to understand the gap/flaw in the officials reasoning. Could someone please explain that?
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I see there are expert explanations. What do you feel is lacking?

PS.
This is a very hard question. I would not recommend wasting your time on trying to dissect a hard question until you feel comfortable with medium and easy because the skills required for those two groups are very different.
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Urban rail systems have been proposed to alleviate traffic congestion 15 Sep 2025, 21:00
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Hello bb KarishmaB GMATNinja egmat
I wasnt able to understand the gap/flaw in the officials reasoning. Could someone please explain that?
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Looking at this question, I can see why identifying the flaw might be challenging! Let me help you understand the gap in the officials' reasoning through a systematic approach.

Understanding the Argument Structure:

Original Claim: Urban rail systems are ineffective at reducing traffic congestion Evidence: A city opened 3 rail branches but lost 3,100 rail commuters while employment grew by 96,000 Officials' Counter: "But commuting trips are only 20% of urban travel!"

The Key Insight - Think About Rush Hour:

Here's a question to consider: When you think about traffic congestion, when is it worst? During rush hours when people commute to/from work, right?
Now, even though commuting trips might only be 20% of total daily trips, ask yourself:
  • Do these 20% of trips happen randomly throughout the day?
  • Or do they all happen at the same time (8-9 AM and 5-6 PM)?

The Fatal Flaw:
The officials assume that if commuting = 20% of trips, then commuting = 20% of congestion. But this is wrong!

Why? Because congestion isn't about the percentage of total trips; it's about how many cars are on the road at the same time.

Consider this analogy:
  • A restaurant serves 100 customers daily
  • Only 20 customers (20%) come for lunch between 12-1 PM
  • But those 20 customers arriving simultaneously create 80% of the restaurant's crowding problems!

Similarly, commuting trips might be only 20% of urban travel, but because they're concentrated during peak hours, they could easily cause 50%, 60%, or even 80% of traffic congestion.

Why Answer Choice (C) is Correct:"fails to consider that commuting trips may cause significantly more than 20 percent of the traffic congestion"

This directly identifies the gap: The officials wrongly equate trip percentage with congestion percentage, ignoring the timing concentration effect.

Why Other Options Don't Work:
  • (A) - Officials aren't disputing the statistics
  • (B) - They're using data from the specific city mentioned
  • (D) - They're defending against this specific example, not making generalizations
  • (E) - While non-commuter usage matters, it doesn't address the core congestion issue

You can check the detailed explanation here (it will help you understand how to "pre-think" the solution for questions like these).

Strategic Takeaway for Similar Questions:
When evaluating counter-arguments in CR questions, always check if the response:
  1. Actually addresses the original concern
  2. Makes unwarranted assumptions about proportionality
  3. Confuses correlation with causation

In this case, the officials' "20%" statistic sounds relevant but actually sidesteps the real issue - whether the rail system reduces congestion, not whether it serves non-commuters.
Remember: Percentage of trips ≠ Percentage of congestion!
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Urban rail systems have been proposed to alleviate traffic congestion 16 Sep 2025, 06:05
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Why is D wrong?fails to show that the decline in the number of urban rail commuters in one U.S. city is typical of U.S. cities generally
This would be a criticism of the critics’ original evidence, not of the officials’ response.
The critics used one city as evidence that urban rail systems don’t work.
A flaw in their argument would indeed be: “You can’t generalize from one city to all U.S. cities without showing it’s typical.”

But the question stem says:
“The response of the officials ... is most vulnerable to criticism...”
So the test-taker must evaluate the officials’ rebuttal, not the critics’ evidence.

When you see “X’s response is vulnerable...” check whose argument the question wants you to critique. If the choice attacks the other side, not the one named in the question stem, it’s wrong.
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