These comments are all over the place. If you must look at correlations, there are some more rigorous methodologies to study cell phone use or vehicle weight you can use.
My preference is when you're given historical data is to find a natural experiment and use something like an interrupted time series regression. For example, if there are two cities with mostly similar characteristics but one criminalizes cell phone use more explicitly, you can compare statical differences in accidents while controlling for historical trends.
And that's just from the top of my head. That said, there's fairly concrete evidence without looking at correlations... at least, we know heavier cars are much more lethal from physical tests, no correlation needed. The historical trends also have conflicting factors too, like safety features; e.g. mandatory rear view camera in... 2017, I think it was? So yeah, things can also just be murky if you don't isolate your variables.