49 CFR § 325.77 - Computation of open site requirements—nonstandard sites.

---
identifier: "/us/cfr/t49/s325.77"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "49 CFR § 325.77 - Computation of open site requirements—nonstandard sites."
title_number: 49
title_name: "Transportation"
section_number: "325.77"
section_name: "Computation of open site requirements—nonstandard sites."
chapter_name: "FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "A"
subchapter_name: "GENERAL REGULATIONS"
part_number: "325"
part_name: "COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 4917; 49 U.S.C. 301; and 49 CFR 1.87."
regulatory_source: "40 FR 42437, Sept. 12, 1975, unless otherwise noted."
cfr_part: "325"
---


# 325.77 Computation of open site requirements—nonstandard sites.

(a) If the distance between the microphone location point and the microphone target point is other than 50 feet (15.2 m), the test site must be an open site within a radius from both points which is equal to the distance between the microphone location point and the microphone target point.

(b) Plan view diagrams of nonstandard test sites are shown in Figures 3 and 4. Figure 3 illustrates a test site which is larger than a standard test site and is based upon a 60-foot (18.3 m) distance between the microphone location point and the microphone target point. (See § 325.79(b)(1) for an example of the application of the correction factor to a sound level reading obtained at such a site.) Figure 4 illustrates a test site which is smaller than a standard test site and is based upon a 35-foot (10.7 m) distance between the microphone location point and the microphone target point. (See § 325.79(b)(2) for an example of the application of the correction factor to a sound level reading obtained at such a site.)