Case Study:

Waterloo, Iowa

Application

The U.S. 63 noise analysis showed a maximum of 64 dBA near the centerline of the highway, attenuating to 55 dBA by 1,000 feet away from the highway. For comparison, standards established by the Minnesota Pollution Control Agency suggest that in residential areas, noise levels should not exceed 65 dBA more than 10 percent of the time during the daytime, and should not exceed 55 dBA more than 10 percent of the time at night. Additional noise standards are shown in Table 1.

Table 1. Maximum Allowable Noise Level Outside Buildings, Minnesota

Source: Minnesota Department of Transportation as reported in Forkenbrock and Schweitzer (1997).

Note: L50 is the decibel level which should not be exceeded more than 50 percent of the time. L10 is the decibel level that should not be exceeded more than 10 percent of the time.

By using the GIS to overlay noise contours on population data, the authors estimated that the daytime Minnesota standard was exceeded for 189 low-income people (or 16 percent of the population in the study area) and 499 minority people (42 percent of the population).

The authors also tested a hypothetical scenario in which heavy truck traffic was added to U.S. 63 to approximate the effect of a significant amount of industrial development along the route. The model shows that even if there were a significant increase in truck traffic during the day, noise levels would remain below federal standards.

The air pollution analysis showed a maximum CO concentration of 31 ppm, compared to the Federal one-hour standard of 35 ppm. The analysis also showed a PM level of 12.5 ug/m3, well below the maximum allowable annual mean of 50 ug/m3.

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