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• Immediately after Con Edison experienced a power anomaly at 8:25 p.m. that temporarily interrupted power to subway signals and communications, severely impacting seven subway lines, a battery-powered backup system engaged to keep the system fully operational. 
• Two backup emergency generators are designed to operate automatically when it senses a loss of power, which would replace the battery power. 
• The system is designed to return to Con Edison power when it becomes available, but that did not occur. 
• An alert system that should have informed subway management of the failures did not provide alerts, resulting in those managers believing that systems were operating properly when in fact batteries continued to energize the system for approximately 45 minutes. 
• At 9:14 p.m. the batteries, which are not designed to provide long-term power, ran out causing the major service interruption. 
• HDR is one of two engineering firms that will conduct an independent review of what occurred and will make recommendations for any systemic changes to minimize the likelihood this incident happens again.