Question 23·Medium·Text Structure and Purpose
Some city officials believe that adding lanes to major roads will relieve congestion. Yet studies of Dallas, Atlanta, and Los Angeles reveal that within a few years of expansion, traffic volume rises to fill the new capacity, leaving commute times unchanged or worse. This phenomenon, known as induced demand, suggests that building more roads treats a symptom rather than the cause. Instead, officials should invest in reliable public transit and mixed-use zoning that reduce residents’ reliance on cars.
Which choice best states the main purpose of the text?
For main purpose questions, first read the short passage all the way through and, before looking at the choices, quickly state in your own words: "This passage is mainly saying that…" Then check the first and last sentences to confirm that summary. When evaluating choices, eliminate any that (1) focus only on a detail or example, (2) introduce ideas not in the passage (like popularity or procedures), or (3) get the passage’s attitude or claim wrong. Choose the option that best matches your own one-sentence summary of the entire passage, not just one part of it.
Hints
Look at the beginning and the end
Reread the first and last sentences. What idea does the author introduce at the start, and what recommendation or conclusion do they make at the end?
Ask what role the city examples play
Think about why the author mentions Dallas, Atlanta, and Los Angeles. Are these cities the main topic, or are they being used to support a broader point?
Focus on what is being argued about solutions
Consider whether the passage is mainly giving neutral information, comparing popularity, describing procedures, or arguing about whether a certain traffic solution works.
Step-by-step Explanation
Identify the passage’s main claim
Look at the first and last sentences to understand the big idea.
- First sentence: some officials think adding lanes will relieve congestion.
- Last sentence: the author says officials should instead invest in public transit and mixed-use zoning.
So the passage is about whether adding lanes is a good solution and what should be done instead.
Notice how the middle sentences support or challenge that claim
The middle of the passage describes studies of Dallas, Atlanta, and Los Angeles:
- After road expansion, "traffic volume rises to fill the new capacity, leaving commute times unchanged or worse."
- This result is labeled "induced demand" and said to show that "building more roads treats a symptom rather than the cause."
This means the evidence is used to show that adding lanes does not actually solve congestion.
Translate the passage into your own short summary
Combine what you saw:
- Some officials think more lanes will fix traffic.
- Evidence from several cities shows that traffic just grows to fill the new lanes.
- This phenomenon (induced demand) means road expansion doesn’t really solve the problem.
- The author then recommends other strategies (public transit and mixed-use zoning).
So the passage’s purpose is to make an argument about the effectiveness of road expansion and to point toward better approaches.
Match that summary to the answer choices
Now compare your summary with each option:
- The only choice that matches the passage’s focus on induced demand showing that road expansion does not effectively reduce congestion is B) To explain why induced demand makes road expansion an ineffective solution to congestion.