Total traffic injuries and fatalities in NYC declined in the first three months of 2015 compared to the same period last year, according to NYPD crash data. While it’s too early to isolate the effect of the city’s speed camera program on street safety, the available evidence strongly suggests cameras are a factor in the city’s continued improvement.

And yet more than half the speed cameras at NYC DOT’s disposal are still dormant. If speed cams are saving people’s lives, then the sloth-like rollout is also costing lives.

As of the end of March, there were 40 traffic fatalities in NYC this year, compared to 51 through March 2014, a 22 percent decrease. Motorists killed 24 people walking and biking through March, compared to 33 for the same period last year, a 27 percent decline.

Injuries, which are less prone to random variation, were also down through March. The total number of people injured in crashes decreased by 6 percent from the same period in 2014, and injuries to pedestrians and cyclists dropped 14 percent.

What’s making streets safer? The increase in speed cameras, paired with the lowering of the city’s default speed limit to 25 mph last fall, is the single most significant change to NYC’s streets in the past year.

There were 20 functioning speed cameras in the city as of last fall, and by the end of 2014, 49 cameras were operational, according to the Daily News. That year, cameras nabbed almost four times as many speeding drivers as NYPD, despite Albany-imposed restrictions that limit camera tickets to school zones during school hours.

A four-month DOT study found that speeding decreased 60 percent at locations with cameras. A WNYC data analysis found that crashes resulting in injury fell 13 percent within 500 feet of fixed camera locations in the last four months of 2014, compared to the same period in 2013.

DOT is now using 63 of the 140 cameras allowed by Albany, and plans to have all cameras operating by the end of 2015. Should it take the city that long to place a few dozen cameras when lives are at stake?