A signature Bloomberg-era public health initiative—the city's roll-out of dozens of Green Carts to sell fresh produce in low-income food deserts—is a success, according to a new study that finds the carts are serving needy New Yorkers and boosting small business owners.

However, the study located only a third of the carts for which permits were issued.

"Green Carts are all located in the low-income neighborhoods targeted by the [health department], exhibiting characteristics associated with food deserts," the report by Columbia University's School of International and Public Affairs found. "Most Green Carts are located in areas with relatively low produce store density, indicating that Green Carts is achieving its goal of reaching populations in high need neighborhoods."

More than 40 percent of Green Cart customers early less than $25,000 a year and more than two-thirds earn less than $50,000, and roughly a fifth get public assistance.

Seventy-one percent of customers said they at more fresh fruits and vegetables thanks to the Green Carts.

Since 80 percent of vendors say they're turning a profit, 75 percent feel their Green Cart experience is equipping them to open a larger business and 56 percent of vendors expect to be operating a year from now (with another 31 percent saying they "may" be operating in a year's time), the report concludes that the program is "providing entrepreneurial opportunities to vendors and is economically viable in the long term."

The city initially allocated 1,000 Green Cart permits, but many were not issued. The SIPA study was based on responses from the owners of 166 carts out of 491 permits that were actually assigned to vendors.

Of the 350 permits allocated for Brooklyn, for instance, 132 were ultimately issued, but only 19 carts were located for the SIPA study. Fifty-eight carts were active in the Bronx, 45 in Manhattan and 22 in Queens. No cart was operating in Staten Island.

It's hard to say what the low number of located carts means. The report suggests that, because of the low ($75) cost of a permit, "many vendors can easily purchase a permit, but do not actually operate a Green Cart." It's also possible there are other active carts that simply couldn't be located. And of course, some carts may have operated for a time and failed.

"The city does not currently track operational Green Carts by location," the SIPA report reads. "The number of valid permits does not equal the number of Green Carts in operation. As a consequence, no one knows exactly where a Green Cart is on any given day or how many Green Carts are actually in operation."

The SIPA study recommends that the city track carts better, as well as do more to target new Green Carts to areas that still need them.