This data describes transportation noise pollution at various geographic levels in Iowa. The data comes from the Bureau of Transportation Statistics, link found below. Transportation noise pollution is estimated by BTS for roads and aviation.
https://data-usdot.opendata.arcgis.com/datasets/a4bc5afb6132423ab4432f1a84d9626f
Relative noise is measured by expected amount of noise for the given area based on the state average. An area with a relative noise score of 2 has twice as much noise pollution as expected while an area with a score of 0.5 has half as much noise pollution as expected. An area with a score of 1 has exactly as much noise pollution as expected.