What study design would help determine if speed feedback signs caused a reduction in fatalities?

• A. Cross-sectional survey
• B. Before-after study with a control location
• C. Case-control study
• D. Simple observation

Answer: (B)

Determining whether speed feedback signs reduce fatalities requires a design that compares outcomes over time and against a similar area without the signs. A before-and-after study with a control location does exactly that: it looks atFatalities before the signs were installed and after, both at the site with the signs and at a comparable location without them. If the drop in fatalities at the sign site is greater than any change seen at the control site, this strengthens the case that the signs contributed to the reduction, while helping to account for other factors that could influence crashes over time, such as weather, traffic volumes, or broader safety campaigns.

Cross-sectional surveys can’t show changes over time or establish a cause-and-effect sequence. A case-control study is more about investigating factors linked to individual fatalities rather than evaluating the impact of an intervention on population-level outcomes. Simple observation lacks a before-and-after comparison and a control, so it can’t separate the effect of the signs from other time-related influences.