The city’s 311 service now handles 15 million calls a year, up from 1.2 million when it launched five years ago, according to a report released yesterday by the Independent Budget Office.

Making good on a campaign promise, Mayor Bloomberg launched 311 to give New Yorkers an alternative phone number to 911 for nonemergency complaints and information requests. Mr. Bloomberg said the system would streamline a “frustrating bureaucracy” New York residents faced when dealing with city agencies. Previously, about 40 separate help lines and the Mayor’s Action Center handled complaints. Several major cities had already implemented 311 by the time Mayor Bloomberg introduced the service, including Chicago, Baltimore, and Detroit.

The added service has not come without cost. Since 2003, 311 has more than tripled its operating budget, which is expected to reach $57.6 million this year, up from $46.6 million in 2007 and $16.9 million in 2003, according to the IBO.

The increasing costs are largely the result of the growing number of 311 calls, requiring large increases in city staffers to handle them. The service’s workforce grew to 461 in 2007 from 193 in June 2003. While budget woes threaten to cut staff at many city agencies, 311 is expected to grow to employ some 544 workers by the end of the current fiscal year, according to the IBO. As staff has increased, wait times on calls have improved. In 2007, 96% of 311 calls were answered in 30 seconds or less, up from just 63% in 2005, and 86% in 2006.

According to the IBO report, noise complaints are the most common reason for 311 calls, with 374,351 in 2007. New Yorkers made 262,583 calls for bus and subway information, and 249,624 for information on parking violations, the second- and third-most popular uses of the service.