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National Electric Transmission Congestion Studies

National Electric Transmission Congestion Studies

Section 216(a) of the Federal Power Act, as amended by the Energy Policy Act of 2005, directs the U.S. Department of Energy (DOE) to conduct a study every three years on electric transmission congestion and constraints within the Eastern and Western Interconnections. Based on this study, and comments concerning it from states and other stakeholders, the Secretary of Energy may designate a geographic area experiencing electric transmission capacity constraints or congestion as a "national interest electric transmission corridor" (National Corridor).


Congestion occurs on the nation’s electric transmission grids when actual or scheduled flows of electricity over a line or piece of equipment are constrained below desired levels. These restrictions may be imposed either by the physical or electrical capacity of the line or by operational directives that are created and enforced to protect the security and reliability of the grid. The term “transmission constraint” can refer to a piece of equipment that restricts power flows, to an operational limit imposed to protect reliability, or to a lack of transmission capacity to deliver electricity from existing or potential generation sources without violating reliability requirements.

Because wholesale power purchasers typically seek to buy the least expensive electricity available, if transmission constraints frequently limit the amount of electricity that can be delivered into an area where demand for it is high, the power purchasers must buy more often from higher-cost suppliers, and the result is higher electricity costs for consumers. In more severe congestion conditions, transmission constraints can impair grid reliability by reducing the diversity of available electricity supplies and rendering the area more vulnerable to unanticipated outages of major generators or transmission lines.

Low-level transmission congestion is very common, and it would not be economic or practical to eliminate all congestion. Broadly speaking, there are three ways to mitigate congestion where it is significant enough to merit remediation. These are: 1), reduce electricity demand in the congested area through energy efficiency and demand management programs; 2) build more generation capacity close to the demand area; and 3) build additional transmission capacity so as to enable more electricity to be delivered from distant generators. Electric system planners frequently find that a combination of the three approaches is most desirable.

DOE’s Congestion Studies may contribute information needed to support the future designation of one or more National Interest Electric Transmission Corridors (National Corridors). On the basis of a congestion study, and after reviewing and considering public comments, the Secretary of Energy is authorized but not required to designate related geographic areas as National Corridors. Designation of a National Corridor would have two effects: 1) it would emphasize that the Department considers the particular congestion problem to which the corridor pertains to be sufficiently acute to merit federal concern; and 2) it would enable the Federal Energy Regulatory Commission to exercise “backstop” authority (under conditions specified in the Federal Power Act) to approve the siting of transmission facilities within the area of the corridor. In particular, the Commission may exercise its jurisdiction if a state agency has “withheld approval” for more than one year of an application to site a transmission facility within the corridor.

2015 National Electric Transmission Congestion Study

The National Electric Transmission Congestion Study released in September 2015 seeks to provide information about transmission congestion by focusing on specific indications of transmission constraints and congestion and their consequences. The study focuses primarily on historical trends over the past few years, and looks into the future to the extent possible. It does not apply congestion labels to broad geographic areas such as the “critical congestion areas,” “congestion areas of concern,” and “conditional congestion areas” identified in earlier studies. For analytic convenience, the study’s results are presented and discussed in relation to four large regions of the United States: the West, Midwest, Northeast, and Southeast. The area covered by the Electric Reliability Council of Texas (ERCOT) is excluded by law from this study.

2009 National Electric Transmission Congestion Study

The 2009 National Electric Transmission Congestion Study examines transmission congestion constraints across the Nation and identifies areas that are transmission-constrained. It does not make recommendations concerning existing or new National Corridor designations. Public comments received after the release of the 2009 Congestion Study can be found here.  

2006 National Electric Transmission Congestion Study

The 2006 National Electric Transmission Congestion Study examines transmission congestion constraints across the Nation and identifies areas that are transmission-constrained. Based on this study, two National Interest Electric Transmission Corridors were designated in 2007, but they were invalidated by a federal appeals court in 2011. Public comments and form letters on the 2006 Congestion Study can be found here.