A million times a year, fire trucks are driven into the streets of New York City, usually at breakneck speeds with lights and sirens blaring. The rush is often critical: Firefighters converge on fires, douse the flames and save lives. The same response applies in less serious situations — calls that are not life-threatening, which are expected to reach around 230,000 this year after steadily rising from 41,054 in 1969. But with 35-ton rigs barreling through red lights and forcing traffic off the roads or through busy intersections, accidents occur, sometimes with deadly consequences. Nearly 700 times last year, the city’s fire trucks collided with other vehicles and, occasionally, with one another. Now, for the first time, the Fire Department is re-engineering its approach: Its plan, set to begin on Monday as a three-month pilot program in Queens, is meant to slow firefighters’ responses to certain calls by having them turn off their lights and sirens and follow the usual traffic rules. In 2009, there were 148 accidents involving fire trucks that were responding to calls for things like water and gas leaks, toppled trees, foul odors, false alarms and faulty sprinkler system activations. In October, for example, a ladder truck flipped and skidded into a tree after hitting an engine truck racing to the same nonfire emergency in Brooklyn, pinning a driver in the wreckage and injuring more than a dozen people. For Salvatore J. Cassano, the city’s fire commissioner, the idea to alter the protocols first took root in the 1990s, when he was a division commander in Brooklyn and saw a civilian killed after a fire truck racing to a minor event crashed in the street. “It is long overdue,” Mr. Cassano said. “Often, responding to a call can be even more dangerous for our members than the incident itself,” Mr. Cassano added. “We want to minimize the danger this poses to firefighters and the public.” All-out emergency responses will still apply for fires and medical calls. But in two other areas, the department’s Bureau of Operations will instruct firefighters to modify their responses, a move that runs counter to the department’s longstanding gung-ho culture. Officials have studied the issue for years, issued a report about it, and it has the support of the top staff and field chiefs, Mr. Cassano said. Firefighters on a call that requires a single truck sometimes take the slower, more cautious approach, obeying a so-called 10-20 signal that has been in place in the department for decades, but has not been widely used. For some calls that require several trucks, firefighters in the first truck will still rush out quickly, but the following ones will proceed more slowly until the circumstances become clear. More than 300,000 runs a year, or 30 percent, could be affected, officials said, adding that the change would spare trucks some wear and tear, save money and lessen noise. Operations manuals will not be rewritten. This sort of “go slow” policy has been contemplated by fire commanders for years, and variations of it are used in cities around the nation and the world, said Russell E. Sanders, who retired in 1995 as the top chief in the Louisville, Ky., Fire Department and is now on the staff of the National Fire Protection Association. A similar policy was used in Louisville in the 1970s when the numbers of malicious false alarms mushroomed, and the concept was recently adopted in St. Louis, he said. “I know that in St. Louis, they are calling it, ‘Responding on the Quiet,’ ” Mr. Sanders said. “It is a good, solid firefighter safety policy when research indicates that the risk-versus-benefit analysis cannot justify a full-out, lights, sirens, bust-traffic-signals, do-what-you-have-to response.” Stephen J. Cassidy, the head of the Uniformed Firefighters Association, the union that represents New York City’s 8,800 rank-and-file firefighters, characterized the pilot project as flawed and “just another step” toward closing fire companies, a notion fire officials rejected. Mr. Cassidy said that with underlying pressure on fire companies to cut response times, the go-slow policy represented something of a mixed message. He said accidents could increase if fire companies became confused, or if crews from different boroughs were called in. And in dense city traffic, he said, abandoning the use of lights and sirens could stop rigs cold. “It could take you five minutes to go one block,” he said. Mr. Cassidy also questioned the wisdom of introducing such a policy change when complaints about flaws in the city’s new 911 system are still swirling. Al Hagan, the head of the union representing fire officers, said the real problem in New York City was the new call system. The system, overhauled in May 2009, has police operators relaying information electronically to fire and medical operators, who previously had dealt directly with 911 callers. There have been missteps, including some instances last year of keystroke errors by emergency dispatchers causing fire trucks to race toward the wrong addresses. Now, the new response protocols mean that fire companies will be analyzing the nature of emergencies in real time. “You are dispatching guys to the wrong locations, and sending them with incorrect or insufficient information,” Mr. Cassidy said. “Now, you want to do a modified response plan on the assumption that the information flowing is always accurate, and that is not always the case.” Concerns about overlaying the new protocol onto the recently overhauled 911 system are valid, said Glenn P. Corbett, an associate professor of fire science at John Jay College of Criminal Justice. “The thing for me is, this has to be very carefully done,” Professor Corbett said. “It has to be built up with simple things first. If it was me, I would start it up with a couple of battalions, start it up slow, rather than all of Queens.” Mr. Cassano said the union was “bringing up old issues” in questioning the new dispatch system. He said the pilot plan, which he called a living document, had been modified: for example, it would still be an emergency call if someone got stuck in an elevator. Going forward, Mr. Cassano said he planned to apply the new protocols to some aspects of the department’s Emergency Medical Service, too; 850,000 of its 1.3 million calls for service last year, almost two-thirds, were for situations that were not life-threatening emergencies, officials said. Mr. Cassano recalled a time in city history when fires and false alarms made up the overwhelming majority of calls. But “it’s a different world,” he said. Through last month, there were 19,379 calls for structural fires this year, 14,556 for other fires, 160,739 medical calls, and 162,812 nonmedical and nonfire calls. By AL BAKER