Say it with me: Leading pedestrian intervals.

To rebuild a street with safety in mind, there are a few basic principles—narrow lanes for cars, wide sidewalks for pedestrians, and protected pathways for cyclists.

It’s not rocket science, but it is expensive. In downtown San Francisco, an effort to build a raised bike path and special bus boarding islands along one mile of Second Street—which is part of the city’s “high-injury corridor”—is pegged at $20 million. And, as with most public projects, years of planning, community outreach, and political fanfare have preceded the start of construction itself.

The value of a life may transcend any dollar figure. But at least one traffic intervention can save lives, at low cost and little time: That’s “leading pedestrian intervals,” or LPIs. In traffic-engineering-speak, these are streetlights that give walkers a head-start before cars venture into an intersection. Given even a few seconds of priority, most people wind up at least halfway into the crosswalk—where they’re plenty visible to drivers—before cars are allowed to go straight or make turns (including the ultra-dangerous left).

San Francisco, Los Angeles, and Seattle have all boosted the number of LPIs in busy intersections since adopting “Vision Zero” traffic safety platforms in recent years. But New York City has been a leader, adding 2,201 since 2014 for a total of 2,483 across the boroughs. Now, nearly 20 percent of signalized intersections citywide have LPIs, according to a report by the advocacy group Transportation Alternatives. They give pedestrians a 7- to 10-second head start. Most are located in the city’s highest-risk traffic corridors; a city map shows their remarkable spread over time.

According to a New York City DOT spokesperson, the average cost to reconfigure a crosswalk for an LPI is $1,200. They don’t require any trench digging, concrete pouring, or lane closures. Sometimes new push buttons and controllers are needed; often engineers simply study local traffic patterns and reprogram existing lights.

For such a small cost, the results can be transformative: One paper published by the Transportation Research Board found LPIs can reduce pedestrian-vehicle collisions by as much as 60 percent. In San Francisco, the intersection with the highest rate of pedestrian injuries from left-turn vehicle crashes saw those incidents drop to zero after an LPI was installed. And a 2016 study of 104 intersections by the NYC Department of Transportation found that pedestrian and bike fatalities and severe injuries declined by nearly 40 percent at locations where LPIs have been installed.

What’s more, the dramatic uptick of these head-start lights may be what’s driving a broader decline in pedestrian deaths in New York City, as evidenced by a significant decline in fatal crashes caused by a failure to yield, according to the Transportation Alternatives report.

“The proliferation of LPIs at crash-prone intersections has been among the most effective actions that New York City has taken since Vision Zero was adopted,” said Paul Steely White, the executive director of Transportation Alternatives. “Dollar for dollar, this is a really smart, life-saving investment that ought to be a part of any city’s effort to eliminate traffic deaths.”

New York City has been criticized for stalling on its Vision Zero campaign efforts. Although pedestrian fatalities have significantly declined since 2013, cyclist deaths and injuries are on the rise.

If one project shows what’s needed to protect all commuters, it might be the $100 million ongoing overhaul of Queens Boulevard, the seven-mile, ultra-wide artery known locally as the “Boulevard of Death” for its staggering toll: 185 deaths between 1990 and 2015. Since New York City started a multi-year makeover of the thoroughfare—narrowing lanes, widening sidewalks, and protecting cyclists—guess what? Zero pedestrians or cyclists have died.

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