As part of a comprehensive reference book on environmental impacts in transportation corridors, a practically oriented guide to assessment of noise effects has been prepared for the California Department of Transportation. Among the major areas covered are (1) review of current knowledge of noise and vibration effects associated with highway and rail traffic; (2) provision of methods of estimating exposure levels associated with varying amounts of traffic; (3) relation of expected levels of exposure to anticipated social impacts; (4) explanation of a quantitative Noise Impact Index for evaluating alternative routes; and (5) discussion of measures to mitigate noise impacts. This paper summarizes the findings contained in the guide to noise impact assessment to bring it to the attention of transportation planners and others concerned with assessment of noise effects.