At 2:00 PM on August 14, 2003, approximately 50 million people lost electricity from the Midwest to New York City and up to Ontario. The reason? A high-voltage power line in Ohio brushed against some overgrown trees and shut down causing cascading blackouts throughout the region. Disruptions like this are not only inconvenient, but they can also inflict tens of billions of dollars in losses and are a hazard to public safety.
Until now, there has been little information on why small, localized electrical failures, which are generally inconsequential, can sometimes disrupt large portions of the power grid like the one that occurred in 2003. In research published in the journal Science, Northwestern investigators examined the US–South Canada power grid — the largest contiguous power grid in the world that is amenable to modeling — and estimated the probability that each transmission line would fail in a cascading blackout (see sidebar video).