Under Part 150 federal land-use guidelines, land uses are compatible with noise levels less than which value?

• A. 60 DNL
• B. 65 DNL
• C. 70 DNL
• D. 75 DNL

Answer: (B)

Part 150 uses the Day-Night Average Sound Level (DNL) to judge how surrounding land uses tolerate airport noise. The guidelines place land uses into categories based on DNL. Land uses are normally compatible up to a DNL of 65 dB; from 65 to 75 dB they’re typically considered conditionally compatible with mitigation, and above 75 dB they’re not normally compatible without substantial mitigation. So the value that defines the compatibility boundary is 65 DNL, meaning noise levels below 65 DNL are generally compatible with surrounding land uses.