Does anyone know of projects or safety improvements planned for other Interstates on that list? Or what can be done in general to reduce the accident rate on Interstates?
That assumes that the Interstates on that list are unusually unsafe. ISTM that those Interstates might have many accidents per-mile only because those miles have unusually high traffic volumes, especially compared to Interstates including long rural segments. The article's author (not unreasonably) did not adjust for population, but made no adjustment at all for traffic volumes.
When you adjust for traffic volumes, you might find that lower-volume Interstate segments are the ones where safety improvements might be most cost-effective, saving more lives at less cost.
It doesn't help the article's credibility that Vox says the author is a "graphics reporter", rather than someone with transportation expertise.