Cal. Sts. & High. Code § 216

(a) The noise level produced by the traffic on, or by the construction of, a state freeway shall be measured in the classrooms, libraries, multipurpose rooms, and spaces used for pupil personnel services of a public or private elementary or secondary school if the rooms or spaces are being used for the purpose for which they were constructed and they were constructed under any of the following circumstances:
1. (1) Prior to the award of the initial construction contract for the freeway route and prior to January 1, 1974.
2. (2) After December 31, 1973, and prior to the issuance of a statement of present and projected noise levels of the freeway route by the department pursuant to subdivision (f) of Section 65302 of the Government Code.
3. (3) Subsequent to the construction of the freeway but prior to any alteration or expansion of the freeway that results in a significant and perceptible increase in ambient noise levels in the rooms or spaces.
(b) The measurements shall be made at appropriate times during regular school hours and shall not include noise from sources that exceed the maximum permitted by law.
(c) If the noise level produced from the freeway traffic, or the construction of the freeway, exceeds 55dBA, L10, or 52dBA, Leq., the department shall undertake a noise abatement program in any classroom, library, multipurpose room, or space used for pupil personnel services to reduce the freeway traffic noise level therein to 55dBA, L10, or 52dBA, Leq., or less, by, measures including, but not limited to, installing acoustical materials, eliminating windows, installing air-conditioning, or constructing sound baffle structures.
(d) If the department determines that the construction of the freeway will result in a noise level exceeding 55dBA, L10, or 52dBA, Leq., the department shall complete the temporary or permanent noise abatement program prior to commencing that construction, or as soon as practicable thereafter.
(e) If it becomes necessary to convert the classrooms, libraries, multipurpose rooms, or spaces used for pupil personnel services to other school-related purposes because the freeway traffic noise level therein exceeds 55dBA, L10, or 52dBA, Leq., the department shall pay the cost of the conversions.
(f) If the noise level generated from sources within and without the classrooms, libraries, multipurpose rooms, or spaces used for pupil personnel services exceeds 55dBA, L10, or 52dBA, Leq. prior to construction of the freeway or completion of the alteration or expansion of the freeway, as the case may be, and the noise from the freeway, or its construction, alteration, or expansion, also exceeds 55dBA, L10, or 52dBA, Leq., the department shall undertake a noise abatement program that will reduce the noise to its preconstruction, prealteration, or preexpansion level.
(g) Priority for noise abatement programs shall be given to those public and private elementary and secondary classrooms, libraries, multipurpose rooms, and spaces used for pupil personnel services constructed in conformance with Article 3 (commencing with Section 17280) of Chapter 3 of Part 10.5 of Division 1 of Title 1 of the Education Code or subject to paragraph (3) of subdivision (a).
(h) As used in this section, dBA means decibels measured by the “A” weighting described in Section 3.1 of the American National Standard specification for sound level meters, S1.4-1971, approved April 27, 1971, and published by the American National Standards Institute. L10 is the sound level that is exceeded 10 percent of the time for the period under consideration and is a value which is an indicator of both the magnitude and frequency of occurrence of the loudest noise events. Leq. is the equivalent steady state sound which in a stated period of time would contain the same acoustic energy as the time-varying sound level during the same time period.