Which statement correctly describes the Day/Night Average (DNL) method?

• A. It is the FAA standard method for forecasting cumulative noise exposure under part 150 studies
• B. It forecasts noise exposure based on peak events only
• C. It ignores nighttime noise
• D. It uses instantaneous sound levels rather than averages

Answer: (A)

The Day/Night Average method is the FAA standard approach for forecasting cumulative noise exposure under Part 150 studies. It combines noise over a full 24-hour period using A-weighted sound levels and adds a nighttime penalty to reflect greater sensitivity and sleep disturbance at night. This creates a single metric that captures both daytime and nighttime noise contributions, rather than focusing on a single event or instantaneous levels.

So why this is the best choice: it explicitly accounts for the cumulative impact of noise across the entire day, with a night penalty that heightens the effect of nighttime noise, which is central to why it’s used in Part 150 forecasting. It’s not limited to peak events, it doesn’t ignore nighttime, and it isn’t based on instantaneous levels alone.