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Difficulty: HardIdentifying Necessary Assumptions

City Planner: To alleviate traffic congestion on the downtown bridge, the city council should implement a dynamic toll system that charges higher fees during peak commuting hours. A recent trial of a similar dynamic toll system on the primary highway of the neighboring city of Oakville resulted in a 20% reduction in peak-hour traffic volume within three months. Thus, our implementation of this system will successfully reduce peak-hour traffic on the downtown bridge.

Which of the following statements are necessary assumptions upon which the city planner's argument depends? (Select all that apply)

  1. The commuters who currently use the downtown bridge during peak hours have viable alternatives to paying the higher toll, such as different routes or adjusted travel schedules.Answer
  2. B
    The dynamic toll system implemented in Oakville generated sufficient revenue to cover the costs of its installation and operation.
  3. The reduction in peak-hour traffic on Oakville's primary highway was not primarily caused by an event independent of the toll system, such as a localized economic downturn.Answer
  4. D
    Most commuters who use the downtown bridge during peak hours will switch to public transit if the dynamic toll system is implemented.
  5. E
    The implementation of the dynamic toll system will completely eliminate traffic congestion on the downtown bridge during peak hours.

Answer

The necessary assumptions are that commuters have viable alternatives to paying the toll, and that Oakville's traffic reduction was not caused by an independent event.
The argument depends on two critical assumptions. First, it assumes that local commuters have the flexibility to avoid the toll (viable alternatives); otherwise, they would simply pay the fee and traffic would remain identical. Second, because the argument relies on Oakville as its sole causal evidence, it must assume that Oakville's traffic reduction was actually caused by the toll, not by an independent factor like an economic downturn.

Step-by-Step Solution

1
Identify the core components of the argument.
Premise: Oakville reduced traffic by 20% after implementing a dynamic toll. Conclusion: A similar toll will reduce traffic on the downtown bridge.
Deconstructing the argument is necessary to spot logical gaps.
2
Determine the logical gaps in the reasoning.
The argument assumes the two cities are analogous (commuters can change habits) and that the toll actually caused the reduction in Oakville.
Identifying missing links reveals potential necessary assumptions.
3
Apply the Negation Test to evaluate the options.
Negating the statement about viable alternatives means commuters must drive anyway, preventing traffic reduction. Negating the statement about Oakville's independent event severs the causal link in the premise.
A statement is a necessary assumption if its negation destroys the argument.

Key Concept

Identifying Necessary Assumptions (Defender and Supporter)
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Topics

Identifying Necessary Assumptions

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