Categorical exclusion means a category of actions which do not individually or cumulatively have a significant effect on the human environment and neither an environmental assessment nor an environmental impact statement is required (40 CFR 1508.4).
Categorical exclusions (CEs) are actions which meet the definition contained in 40 CFR 1508.4, and, based on past experience with similar actions, do not involve significant environmental impacts. They are actions which: do not induce significant impacts to planned growth or land use for the area, do not require the relocation of significant numbers of people; do not have a significant impact on any natural, cultural, recreational, historic or other resource; do not involve significant air, noise, or water quality impacts; do not have significant impacts on travel patterns; and do not otherwise, either individually or cumulatively, have any significant environmental impacts (23 CFR 771.117(a)).
Source: US Department of Transportation. Environmental Review Toolkit NEPA Documentation. Accessed on 9 September 2013. Available at http://environment.fhwa.dot.gov