Yes, there are different criteria for different roads. Presence of schools is one of them. In my neighborhood, the speed limit drops to 25 mph through school zones (it's 40-45 mph outside of the school zone).
My understanding is that the 85 pct rule has fallen out of favor outside of highways (where the mode mix is 100% high power automobiles.) I know for my municipality and my state, we set speeds in denser areas based primarily on the mode mix and in less dense areas a balance between vehicle volumes, congestion in surrounding areas, and mode mix.
