The estimation of absolute road traffic noise levels without including the effects of meteorology is thought to be a major source of error in the estimation process commonly used in the United States. In response, the Transportation Research Board-sponsored NCHRP 25-52, Meteorological Effects on Roadway Noise, to collect highway noise data under different meteorological conditions, document the meteorological effects on roadway noise propagation under different atmospheric conditions, develop best practices, and provide guidance on how to (a) quantify meteorological effects on roadway noise propagation and (b) explain those effects to the public. The completed project involved collecting and analyzing 35,000 min of sound and meteorological data at 16 barrier and no-barrier measurement positions adjacent to Interstate 17 in Phoenix, Arizona. This report provides information on the data collection and the modeling recommendations. The database assembled is thought to be among the best available in the United States to permit analysis of meteorological effects on roadway noise. The study recommendations will advance the methodology for estimating the meteorological effects on roadway noise in the United States. © National Academy of Sciences: Transportation Research Board 2019.