During the quarter, our Electric Power segment grew revenues by approximately 55% compared to the same period last year. Our Electric Power segment 12-month backlog as of the end of the third quarter increased nearly 49% and total backlog increased nearly 17% as compared to the third quarter of 2010. We believe we are in the early stages of a major multiyear transmission buildout in the United States and Canada and expect backlog to continue to remain strong throughout 2012. The large electric transmission projects that we are progressing are progressing in a manner that is consistent with the expectations we set on our second quarter conference call without any meaningful delays during the quarter.
During the third quarter, the joint venture including Quanta operating unit, Valard Construction, finalized the contract with BC Hydro for the engineering, procurement and construction of the Northwest Transmission Line. Under our scope of the contract, we will construct the 344-kilometer 287-kilovolt transmission line, which is designated to provide a secure interconnection point for clean energy generation projects and supply electricity to support future industrial developments in Northern British Columbia. We have commenced preconstruction activities but do not expect to move toward full construction until the spring of 2012, with completion expected in the fourth quarter of 2013.
While large transmission projects are grabbing the headlines, we are also experiencing an increase in activity for projects less than $100 million in value that we typically don't announce. For example, AEP awarded Quanta work in 2 states to rebuild a number of transmission lines totaling more than 300 miles, and Oklahoma Gas and Electric recently awarded Quanta the Seminole to Muskogee Transmission Project, which is a 125-mile, 345-kilovolt line. Construction on this project is expected to start in the middle of 2012 with completion expected in late 2013. The aggregate of these projects is approximately $170 million.