Neat idea. Although I think it's basing this mainly (only?) on road and air traffic data. It doesn't seem to include noise generated by the railways--at least where I looked.
It's not supposed to, yet. But that is pretty important. My gf lives in an urban high-rise, and it's not noisy at all, except for the (above-ground at this point) subway that runs right next to the building.
"Road and Aviation Noise in the United States" is at the top.
> future versions of the National Transportation Noise Map are envisioned to include additional transportation noise sources, such as rail and maritime.