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Difficulty: MediumInferring Author Purpose and Intent

Unlike traditional jointed track, continuous welded rail eliminates rhythmic joint gaps by joining steel sections into seamless, miles-long ribbons. Although this smooth design reduces mechanical wear and enables higher train speeds, it introduces acute vulnerability to temperature extremes. In intense summer heat, constrained steel cannot expand longitudinally, generating immense compressive stresses that can suddenly buckle the track laterally. In sub-zero winter conditions, the metal contracts, creating extreme tensile forces that risk brittle rail breaks. Consequently, railroad maintenance crews must prestress and anchor tracks at a specific neutral temperature to prevent seasonal thermal structural failures.

The author wrote this passage primarily to:

  1. A
    argue that railway networks should abandon welded tracks in favor of traditional jointed rails
  2. B
    highlight that continuous welded rails reduce mechanical wear and allow higher train speeds
  3. explain the thermal challenges and maintenance requirements of continuous welded railsAnswer
  4. D
    prove that summer heat causes more severe railway damage than winter freezes

Answer

The author wrote this passage primarily to explain the thermal challenges and maintenance requirements of continuous welded rails.
The passage focuses on the thermal dynamics of continuous welded rail—explaining how expansion in heat causes buckling and contraction in cold causes fractures—and concludes with the maintenance practice used to stabilize the rails. Therefore, the author's primary intent is to explain these specific physical challenges and maintenance measures.

Step-by-Step Solution

1
Analyze the passage structure and topic development
The text briefly introduces continuous welded rail and its benefits, then dedicates the majority of the content to explaining how seasonal temperature shifts cause compressive and tensile stresses, concluding with how crews anchor tracks at a neutral temperature.
Identifying the central topic and how much space is allocated to different ideas helps determine the overarching intent.
2
Evaluate the author's tone and rhetorical function
The tone is objective, technical, and explanatory, focusing on cause-and-effect relationships rather than persuasion or debate.
Recognizing the tone rules out persuasive or argumentative answer choices.
3
Synthesize the main purpose and match with the correct option
The text serves to inform the reader about how temperature variations affect continuous welded rails and why specific maintenance procedures are required to manage these stresses.
The correct choice must capture the full scope of the passage rather than an isolated detail or an unsubstantiated comparison.

Key Concept

Inferring Author Purpose in Technical Explanatory Texts
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Topics

Inferring Author Purpose and Intent

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