Cal. Health & Safety Code § 39940

(a) The state board shall implement a pilot program to determine emissions from locomotives, using wayside remote sensing devices. The objectives of the pilot program are to determine whether remote sensing devices can accurately and replicably determine, with a reasonable level of precision:
1. (1) The levels of nitrogen oxides, particulate matter, and carbon monoxide emissions from locomotives.
2. (2) Whether a locomotive is subject to tier 0, 1, or 2 federal certification standards.
3. (3) Whether the measured results can be calibrated to determine whether the locomotive emissions are above or below the applicable federal emissions certification levels.
(b) The state board shall design and implement the pilot program in consultation with the advisory group established pursuant to Section 39941.
(c) The pilot program shall collect sufficient data to ensure that a representative sample of locomotives operating in the state are tested, so that there is a sufficient basis for the state board to meet the objectives and to make the determinations that are set forth in subdivision (a). Data collection shall, at a minimum, be performed under representative conditions in northern and southern California.