Subject:

INFORMATION: Use of Latest Planning
Assumptions in Conformity Determinations

From:

(Original signed by)
James M. Shrouds
Director of Natural Environment, FHWA

(Original signed by)
Charlotte M. Adams
Acting Director, Office of Planning Operations, FTA

To:

FHWA Division Administrators
Federal Lands Highway Division Engineers
FTA Regional Administrators

The Environmental Protection Agency (EPA) and the U.S. Department of Transportation are issuing a memorandum jointly to clarify our expectations for implementing the transportation conformity rule's requirements for use of latest planning assumptions in conformity determinations. This memorandum also reiterates EPA's expectations for using latest planning assumptions in the development of motor vehicle emissions budgets in State implementation plans (SIPs). The purpose of this memorandum is to clarify the existing requirement that the conformity determination must be based on the most recent planning assumptions (40 CFR 93.110). This guidance also clarifies that the most current information available must be used at the time that the motor vehicle emissions budgets in SIPs are developed.

As assumptions are expected to change over time, it is important that assumptions used in the SIP process and conformity determination be evaluated and updated on a regular basis. Although regularly scheduled updates are not required by the transportation conformity rule, areas are strongly encouraged to review current planning assumptions and strive towards regular 5-year updates of planning assumptions, especially for population, employment, and vehicle registration assumptions. Areas with network-based models should review their assumptions and data used in model validation through the consultation process, and new assumptions and data must be used whenever available. Conformity determinations that are based on assumptions older than 5 years should include written justification for not using more recent information.

This guidance was developed after consulting with transportation and environmental stakeholders, and the final guidance reflects their comments.

This guidance will be available on the Internet at the FHWA's website (http://www.fhwa.dot.gov/environment/conform.htm). If you have any questions regarding this guidance, please contact Cecilia Ho Cecilia.Ho@fhwa.dot.gov of FHWA at (202) 366-9862, or Abbe Marner Abbe.Marner@fta.dot.gov of FTA at (202) 366-4317.

Attachment

cc: Resource Center Directors