This report provides guidelines on the use of tiering to complete the National Environmental Policy Act (NEPA) process for surface transportation projects that require approval by the Federal Highway Administration (FHWA), Federal Transit Administration (FTA), or Federal Railroad Administration (FRA). The report is based on a review of over 20 tiered NEPA studies that have been initiated between 1999 and September 2008 for highway, transit, and passenger rail projects and is accompanied by a technical memorandum that describes the research methodology, and documents key factors associated with the success of tiered studies while identifying the greatest challenges tiered studies faced.