Last year, our city installed protected bike lanes on several major streets. In the six months following installation, reported cyclist injuries on those corridors fell by 20% compared to the same period the previous year. Citywide traffic volume and weather vary from year to year, and some have suggested that fewer people biking or a milder season could explain the decline. Nevertheless, these results indicate that the new protected lanes reduced cyclist injuries.
Which one of the following, if true, most strengthens the argument?
- Bicycle counts on those corridors rose substantially after installation, yet injury totals still fell, indicating a lower injury rate per cyclist. (correct answer)
- A nearby city that did not add protected lanes also saw a drop in cyclist injuries during the same period.
- The city plans to extend the lanes to additional streets next year.
- During the same months, the police department changed its reporting criteria for minor cycling accidents.
- Many cyclists began wearing brighter clothing and new helmets when the lanes were publicized.
Explanation: If more cyclists used the corridors while injuries fell, the per-cyclist injury rate dropped, strongly supporting the lanes as the cause. The other options either offer alternative explanations, are irrelevant plans, or suggest changes that would undermine the causal inference.