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Question

Difficulty: MediumWeakening Arguments

To reduce particulate matter emissions in its central historic district, municipal administrators implemented a initiative replacing heavy diesel delivery vans with electric cargo tricycles for last-mile freight transportation. Six months into the initiative, municipal logs indicated that while total freight delivery volume in the district remained unchanged, total diesel van mileage within the district dropped by 45 percent. City officials concluded from these data that the initiative successfully reduced total freight-related particulate matter emissions generated within the historic district. Which of the following, if true, most seriously undermines the city officials' conclusion?

  1. The transfer hubs where diesel vans unload freight onto electric tricycles are located inside the historic district, and vans idle their engines continuously during transfers, emitting more particulate matter per delivery than when driving.Answer
  2. B
    Electric cargo tricycles produce zero direct tailpipe emissions and generate significantly less brake dust per kilometer than traditional diesel delivery vans.
  3. C
    Air quality monitoring stations in residential suburbs surrounding the city recorded a minor decrease in fine particulate concentrations over the same six-month period.
  4. D
    Merchants in the historic district reported experiencing minor delivery schedule adjustments during the initial weeks of transition to the tricycle delivery system.
  5. E
    Commercial delivery fleets in neighboring municipalities began replacing older diesel vans with hybrid models during the same year.

Answer

The conclusion is most seriously weakened by evidence that diesel vans idle continuously at transfer hubs within the district during cargo transfers, generating more particulate matter per delivery than they saved by driving fewer miles.
The author concludes that total freight emissions in the historic district decreased based solely on a reduction in van driving mileage. The correct answer points out that diesel vans now spend significant time idling their engines at internal transfer hubs while transferring cargo onto tricycles, producing more emissions per delivery during idling than they saved by driving fewer miles. This unconsidered emission source invalidates the assumption that fewer miles driven equals lower overall emissions.

Step-by-Step Solution

1
Identify the premise and conclusion of the argument.
Premise: Diesel van mileage in the historic district dropped by 45% while freight volume stayed constant. Conclusion: Freight-related particulate matter emissions generated within the district decreased.
Understanding the precise gap between the premise (mileage measurement) and conclusion (total emission output) is necessary to evaluate potential vulnerabilities.
2
Identify the implicit assumption linking mileage to total emissions.
The argument assumes that driving mileage is the sole significant source of freight-related emissions in the district and that non-driving emission sources did not increase.
If emissions from other parts of the delivery process (such as cargo transfer idling) increased substantially, reduced mileage would not guarantee reduced overall emissions.
3
Evaluate the answer choices to find the statement that demonstrates overall emissions did not decrease despite reduced mileage.
The statement describing continuous van engine idling at transfer hubs inside the district shows that a new, high-emission activity was introduced, offsetting the savings from reduced mileage.
This directly undermines the logical bridge connecting reduced driving distance to reduced total district emissions.

Key Concept

Weakening Causal and Presumptive Claims by Introducing Unaccounted Offsetting Factors
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Topics

Weakening Arguments

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