Some good tidbits in here. Lots of examples of lower speed limits resulting in safety gains even without additional traffic calming. Again, you need both, but lower speed limits are a good start.

Lower Speed Limits | NHTSA

New York City after default speed limit went from 30 to 25 mph: "total crashes were reduced by an average of 39% on streets that fell within the statutory default speed limit change (unposted streets) compared to streets where the speed limit was unchanged (those with posted limits)."