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neered to support traffic during busy hours with only about 4 percent of calls being blocked (given a busy signal).
Regionally, the experience was even more dramatic. New York City had a 400 percent increase in call attempts during the day. At about 11:00 A.M., the volume was up 1,300 percent for at least one major carrier. Washington, D.C., had a 125 percent increase for the day. New England as a whole saw a 75 percent increase. The cellular system was not engineered for these loads, so call-blocking rates grew accordingly. In New York, 75 percent of calls were blocked (92 percent at the morning peak). In Washington, D.C., 56 percent of calls were blocked.
Wireless Internet—using such devices as Research in Motion’s Blackberry—also rose on September 11. Traffic surged by 60 percent around 10:00 A.M. and stayed high through the early afternoon.7
Although there have been reports that a large number of cellular phone sites were disabled by the collapse of the Twin Towers, the industry maintains that only five sites were damaged in the attacks. In any case, by late afternoon on September 11, a combination of damage to telephone lines and the loss of power caused 160 cell sites in Lower Manhattan to become inoperable (slightly under 5 percent of the New York City cellular infrastructure). Over the hours and days that followed, the cellular operators adopted a variety of measures, such as the installation of temporary sites and the use of alternate radio frequencies, to restore (or in some cases, such as at the Pennsylvania crash site, to increase) capacity. In Lower Manhattan, full capacity was restored within a week.8
Broadcast Television and Radio
Transmission facilities of 9 of the 14 local-area television stations, along with those of 5 local radio stations, were lost when the North Tower of the World Trade Center was destroyed. Of the stations that lost their transmission facilities, only 2 were able to quickly restore service—WCBSTV (Channel 2), which switched to a full-power backup antenna at the Empire State Building, and WXTV (Channel 41). For households that subscribed to cable, there was much less impact: most television stations deliver their feeds to cable operators directly, by way of fiber or microwave links, and the New York cable-system operators reported no service interruptions outside Lower Manhattan. (However, the impact on broad
From reports by carriers to the Federal Communications Commission.
Data from Kathryn Condello, 2001, “Wireless Industry: Impact and Recovery Efforts Summary Report” (presentation to the Network Reliability and Interoperability Council), Cellular Telecommunications and Internet Association, Washington, D.C., October 30.