Detailed CNEL/Ldn roadway noise calculations vs. estimation methods

Roadway traffic noise calculations of the community noise equivalent level (CNEL) and the day-night average sound level (Ldn) metrics are sometimes required for various federal, state, and local government permitting requirements. To complete calculations of these metrics, detailed hourly traffic data is needed and obtaining this data can sometimes be a challenge. This paper explores various estimation strategies that are sometimes employed for situations where this data is not available and compares the estimates against calculations using detailed hourly traffic data to assess their validity. Project examples are provided of various permitting efforts such as those in support of California Environmental Quality Act (CEQA) documents, roadway projects at airports for Federal Aviation Administration (FAA) National Environmental Policy Act (NEPA) documents, and other local permitting requirements.