[apendleton]

They absolutely are, but are rare enough that it's difficult to reach statistical significance when talking in the aggregate. That a particular part of town went from one fatality one year to zero fatalities the next year is probably not evidence of the success of any particular safety-related policy intervention, it's just noise. Studying all crashes provides a proxy that hopefully helps decrease the odds that the fatal ones will occur will making it possible to make robust, data-driven claims about success or failure.

[takk309]

On a project I am currently working on, we saw pedestrian fatalities shift from 7 to 13 in consecutive years. it is a nearly 100% increase but like you said, it is just noise. This is in a city with around 100,000 residence. Convincing politicians that it is just noise is a whole different story.