As a next step, I suggest calculating the actual rate of fatalities in a particular location vs. some naive estimate for that area, based on traffic counts, car utilization, or nearby population. This will highlight places that have a higher-than-expected number of fatalities.
Some of these places can already be seen visually. For example, Florida is blotted in red even though the population is concentrated around the coasts and bays and the Orlando area; therefore US 301 and other 'interior' portions are more dangerous than population alone would explain.
The Carolinas are similarly covered, well-outside of the Crescent from Raleigh-Durham through the Triad to the Charlotte suburbs. California's Central Valley looks particularly dangerous too, despite most of the traffic sticking to the far western edge with I-5, or the eastern valley floor where the built-up areas are.