Congestion Measures for Organized Markets in the U.S.

Transmission lines deliver electricity that is generated at power plants to loads. When there is not sufficient transmission capacity to schedule or transport all desired electricity transfers, the transmission system is constrained, and the particular line, flowgate or interface is congested. While it is useful to measure congestion for several reasons—to identify where and how much congestion exists and how this changes over time, to determine whether or what to do about it, and to assess the effectiveness of actions taken—it is challenging to measure congestion in a meaningful and consistent way across markets or over time in the same market. This paper examines current public reporting of congestion measures for organized markets in the U.S., and what these measures can and cannot tell us about congestion across regions or over time in the same region.