The majority of heavy trucks operating on the highway either cross state lines or are transporting goods that cross state lines, and so can be considered to be engaged in interstate commerce. As such they are subject to federal regulations, which, if applied to noise emissions, would succeed not only in reducing the noise impact for communities close to heavily traveled highways, but also in using the power of federal preemption to provide a consistent set of noise standards throughout the nation. The mandate for federal action was provided in Section 18 of the Noise Control Act of 1972 which required the Environmental Protection Agency to develop regulations governing the noise emission of motor carriers engaged in interstate commerce. The first step in the development of the regulations by EPA was a definition of the noise characteristics of heavy trucks as they operate on the highway. This information was required to provide baseline data for the existing fleet of trucks and to indicate the modes of operation for which noise regulations would be most applicable. Accordingly, a measurement survey was conducted to sample truck noise levels in different parts of the country under different operating conditions, the results of which would also indicate the effectiveness of certain existing state regulations.