Road Map

The threshold margin of each hour for each subregion is calculated for comparison. A threshold margin, sometimes called a reference margin or planning margin, is the margin needed to maintain reliability in a system. The first chart shows what the overall average threshold margin should be for each subregion by year. The second and third charts show the monthly average threshold margin and the hourly margin, respectively.


The overall annual weighted threshold margin for the Western Interconnection is about 16%. The threshold in the spring months is closer to 20%; threshold for the summer months drops down to 14%.

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Clicking a region on the map will change the charts to show that area's information. Clicking the same area again will switch the charts back to the overall Western Interconnection results.