Yea, I don't know I disagree. The denominator should always be just be population. I don't want to use sprawl as some sort of justification for more deaths per capita. Sprawl should be reduced and/or mitigated somehow.
For example, the risk of a car crash should be near zero if the distance driven is also zero. But even in the safest of vehicles, driving 100KM, 1,000KM, or 10,000KM+ each are going to have higher rates of accidents assuming real-life road conditions.
In the US, on average, people need to travel further to get to their destinations, and so on average I'd expect car accident and death statistics to likewise be higher.
I'm very in favor of reducing urban sprawl, utilizing public transit, etc., but in present state the US has vast quantities of existing road networks which can't be consolidated or mitigated overnight, so the next best way to improve those statistics would be improving traffic controls, vehicles, safety features, etc.
But state and federal governments should absolute zero-in on reducing sprawl and travel distances and those actions should've started yesterday and they should stay laser focussed on reducing driving distances (especially for non-leisure reasons)
Many of the most effective and efficient measures to reduce traffic fatalities work by reducing traffic. For example, promoting public transit. However, if you measure fatalities per kilometer these highly effective mechanisms have no effect on the metric.