It is a small but subtle change that has been happening at selected intersections throughout D.C. — a change in the timing of crosswalks that traffic safety officials hope will reduce the number of pedestrian injuries.

In the transportation world, it’s known as the LPI or Leading Pedestrian Interval. For the rest of us, it is simply this: traffic signals are changed to give pedestrians a three- to 10-second head start before cars begin moving. As a pedestrian you are no doubt familiar with stepping into a crosswalk only to have a left- or right-turn making car halfway into the crosswalk before you’ve stepped off the curb. The LPI is designed to give walkers a head start.

Major cities including Chicago and New York are also using the LPI strategy.

If you drive along the 15th Street corridor or near the U Street/Cardozo Metro, you may have noticed slight change. D.C. officials began piloting the program in 2010 with the goal of having it in at least 100 intersections by 2012. Monica Hernandez, a spokeswoman for the D.C. Department of Transportation said while no studies have been done about the effectiveness of the crosswalk strategy, anecdotal evidence suggests it is helping. A 2004 study by the Institute of Transportation Engineers found that the delay helped reduce pedestrian crashes at intersections by 5 percent. Officials at DC DOT said at least three years of data is needed to measure the effectiveness of such changes.

LPI’s are just one in a number of strategies that D.C. officials are using to reduce pedestrian accidents. In Cleveland Park, officials have installed a “High-Intensity Activated crossWalK — or HAWK signal to make it easier for pedestrians to cross busy streets.

This post has been updated.