City pedestrians tempted to test the stoplight and scurry across the street will now know exactly how long they have to reach the other side — at least at one intersection in each borough.

Mayor Bloomberg yesterday announced a six-month pilot program that will study the impact of pedestrian signals that count down the seconds before the flashing hands turn a solid red.

Department of Transportation officials picked a busy intersection in each of the five boroughs to try out the new signals, which they hope will discourage New Yorkers who are set on beating them and risk getting caught in traffic.

The technology is used is several major American cities already, but officials in New York acknowledge that in a city where flouting pedestrian signals is akin to a birthright, the change may not make a difference.

“It would take a world-class psychologist to understand and describe the way New Yorkers cross busy intersections such as this one,” the mayor said as he stood on the corner of Kings Highway and Coney Island Avenue in Brooklyn, where the first countdown signal was installed yesterday.

The city contracted with an engineering consulting firm, Greenman Pedersen Inc., to study the effects of the new signals. Engineers with the firm observed the five intersections for six months before the switch, studying to what extent pedestrians react to the current signals. They will do the same during the next six months before the city decides whether to expand the initiative.

Traffic fatalities have dropped in recent years, reaching 156 in both 2004 and 2005, the lowest total since 1910, Mr. Bloomberg said. He said the city was keeping pace with that total this year.

Officials chose the intersection at Kings Highway and Coney Island Avenue because a large senior citizen population lives in the area, the transportation commissioner, Iris Weinshall, said. Some studies in cities that now use the countdown signals have shown that elderly pedestrians routinely underestimate the amount of time it takes to cross the street, Ms. Weinshall said.

The countdown on the new signals will begin once the “walking man” sign switches to the flashing hand, ending when the hand turns a solid red. The amount of time for each signal will not change, and the countdowns are at least 15 seconds at each of the intersections used for the trial program.

“When the flashing, ‘don’t walk’ signal starts, we hope the countdown will cause people who haven’t stepped off the curb to think twice before doing so,” Mr. Bloomberg said.

The new signals appeared to cause some initial confusion yesterday. Teenagers at the Kings Highway intersection could be seen explaining the countdown to elderly pedestrians waiting at the light. Even a few of the younger New Yorkers were skeptical about the new technology.

“I don’t think it’s the greatest thing,” a student at the nearby Yeshiva Shaare Torah Boy High School, Joseph Sutton,16, said. “I’m going to underestimate it. Three seconds left, and I’m going to dash across, and then who knows?” Another Shaare Torah student, Leon Tawil, 15, said he welcomed the countdown signals, recalling how he broke his leg after being struck by a car while crossing a nearby intersection two years ago. “I didn’t see the blinking light stop,” Leon said. The new technology “could save a lot of lives,” he said.

Other cities that have already installed countdown signals include Washington, D.C., Boston, San Francisco, Las Vegas, and even Albany. A spokeswoman for Washington’s Department of Transportation, Beauty Stephens, said the signals have been in place for more than a year and have been received well. Some intersections heavily populated by seniors have lights with longer countdowns, Ms. Stephens said.

Officials in San Francisco began installing the countdown lights in 2001, and studies have shown a reduction in pedestrian collisions and an increase in compliance with the signals, a transportation spokeswoman, Margaret Lynch, said.

New York’s pilot program will cost the city $186,000. There are more than 100,000 pedestrian signals citywide, and a full conversion would cost as much as $30 million. But with the city’s many small streets and quiet intersections, that is unlikely to happen. “It doesn’t make sense for all of them,” Ms. Weinshall said.

Besides the Kings Highway location, the other trial intersections are: 8th Street and Sixth Avenue in Manhattan; Hylan Boulevard and New Dorp Lane in Staten Island; Hillside Avenue and 179th Place in Queens, and Southern Boulevard and East 149th Street in the Bronx. The intersections were chosen for various reasons, but all of them are considered heavily trafficked.

Some cities also have audible beeping sounds on signals for pedestrians who are blind. New York already has some audible signals, Ms. Weinshall said, but there are currently no plans to add more. “Some of the audibles are very annoying,” she said. “People have asked us once we put them in to take them out, which we’ve had to do.”