There are three classes of actions which prescribe the level of documentation required in the NEPA process.
(a) Class I (EISs). Actions that significantly affect the environment require an EIS (40 CFR 1508.27). The following are examples of actions that normally required an EIS:
(1) A new controlled access freeway.
(2) A highway project of four or more lanes on a new location.
(3) Construction or extension of a fixed transit facility (e.g., rapid rail, light rail, commuter rail, bus rapid transit) that will not be located within an existing transportation right-of-way.
(4) New construction or extension of a separate roadway for buses or high occupancy vehicles not located within an existing highway facility.
(b) Class II (CEs). Actions that do not individually or cumulatively have a significant environmental effect are excluded from the requirement to prepare an EA or EIS. A specific list of CEs normally not requiring NEPA documentation is set forth in Sec. 771.117(c) for FHWA actions or pursuant to Sec. 771.118(c) for FTA actions. When appropriately documented, additional projects may also qualify as CEs pursuant to Sec. 771.117(d) for FHWA actions or pursuant to Sec. 771.118(d) for FTA actions.
(c) Class III (EAs). Actions in which the significance of the environmental impact is not clearly estabilished. All actions that are not Class I or II are Class III. All actions in this class require the preparation of an EA to determine the appropriate environmental document required. [52 FR 32660, Aug. 28, 1987, as amended at 74 FR 12529, Mar. 24, 2009; 78 FR 8983, Feb. 7, 2013]