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?
- 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.Cevap
- BElectric cargo tricycles produce zero direct tailpipe emissions and generate significantly less brake dust per kilometer than traditional diesel delivery vans.
- CAir quality monitoring stations in residential suburbs surrounding the city recorded a minor decrease in fine particulate concentrations over the same six-month period.
- DMerchants in the historic district reported experiencing minor delivery schedule adjustments during the initial weeks of transition to the tricycle delivery system.
- ECommercial delivery fleets in neighboring municipalities began replacing older diesel vans with hybrid models during the same year.
Cevap
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.
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Weakening Causal and Presumptive Claims by Introducing Unaccounted Offsetting Factors