Passage Summary: Robert thinks the city should put in speed bumps to stop speeders since there aren't enough police. Sheila disagrees, arguing that speed bumps actually make speeding cars more dangerous by making drivers lose control.

Conclusion: The city should not install speed bumps on residential streets because they are a bad idea.

Reasoning: Drivers who are already speeding are likely to lose control of their vehicles when they encounter a speed bump.

Analysis: In this dialogue, Sheila's statement functions as a counter-premise intended to undermine Robert’s proposal. To identify its role, notice that she explicitly labels Robert's plan a 'bad idea' and then provides her statement as the supporting evidence for that judgment. It serves as a reason to reject the conclusion of the first speaker by introducing a negative unintended consequence. It's a classic case of one person proposing a solution and another pointing out a fatal flaw in the execution.