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Difficulty: MediumMost Strongly Supported Questions

When a city installs automated red-light cameras at an intersection, the number of right-angle collisions typically decreases significantly, as fewer drivers attempt to run the red light. However, at intersections where these cameras are installed, the total number of collisions often remains unchanged or even increases. This is because the decrease in right-angle collisions is usually offset by a substantial increase in rear-end collisions, which happen when drivers brake abruptly to avoid being ticketed. Traffic safety data indicates that rear-end collisions are, on average, much less likely to result in severe injuries than right-angle collisions are.

Which one of the following is most strongly supported by the information above?

  1. A
    Most of the collisions that occur at intersections equipped with automated red-light cameras are rear-end collisions.
  2. B
    If a city removes automated red-light cameras from an intersection, the number of rear-end collisions at that intersection will decrease.
  3. The installation of automated red-light cameras at an intersection tends to reduce the overall number of severe injuries resulting from collisions at that intersection.Answer
  4. D
    Drivers who brake abruptly at red-light cameras are less likely to receive a traffic ticket than drivers who attempt to run the red light.
  5. E
    Across a typical city, the total number of severe injuries caused by right-angle collisions is greater than the total number caused by rear-end collisions.

Answer

The installation of automated red-light cameras at an intersection tends to reduce the overall number of severe injuries resulting from collisions at that intersection.
The text demonstrates a shift in the composition of accidents at intersections with red-light cameras. While the total number of accidents stays the same or goes up slightly, the proportion shifts away from right-angle collisions toward rear-end collisions. Because the text explicitly states that rear-end collisions are 'much less likely to result in severe injuries', substituting a more dangerous accident type for a less dangerous one—even if the total number of accidents remains constant—strongly supports the inference that the overall number of severe injuries will decrease at these locations.

Step-by-Step Solution

1
Analyze the causal relationships presented in the stimulus.
Installing cameras causes right-angle collisions to decrease and rear-end collisions to increase.
Understanding the direct effects of the cameras is necessary to evaluate the outcomes.
2
Evaluate the net effect on the total volume of collisions.
The total number of collisions remains unchanged or increases slightly because the rise in rear-end collisions offsets the drop in right-angle collisions.
This establishes that the overall frequency of accidents does not drastically drop, meaning any reduction in injuries must come from the change in accident *type*.
3
Combine the frequency data with the severity data provided at the end of the stimulus.
The intersection is experiencing roughly the same number of total accidents, but a large portion of highly dangerous accidents (right-angle) has been replaced by less dangerous accidents (rear-end).
Synthesizing frequency with severity allows us to draw a strongly supported conclusion about the overall injury rate.
4
Formulate the most strongly supported inference.
Because the new mix of accidents is less prone to causing severe injuries, the overall number of severe injuries at that intersection likely goes down.
This directly matches the correct answer choice.

Key Concept

Synthesizing shifting proportions (accident types) with differing rates (injury likelihood) to infer a net outcome.
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