Surveys of 29 residents 31/2 months before and 21 residents after the May 2011 cleanup found that those near the greened lots felt safer. The surveys did not mention the lots.
"I can't stress enough how important feeling safe in your neighborhood is," said Gina C. Garvin, lead author of the paper, published in the journal Injury Prevention. Existing evidence clearly shows that the perception of safety is linked to health outcomes, she said. "If we can do something to the environment to make people feel safer, then we can really have an impact on their overall health."
This study, like the previous research by Charles Branas, a senior author on the new paper, also looked at crime rates. While the earlier work showed a significant decline near greened lots, this one was too small - comparing just one greened "cluster" of lots with another ungreened - to find statistically meaningful results, although the downward trend was the same.
The study was intended as a pilot effort; a follow-up with hundreds of lots is being planned.
Robert J. Sampson, a sociologist at Harvard University who studies neighborhoods, crime, and the social organization of cities, said that he was looking forward to the larger study but that the findings that people felt safer after improvement of nearby lots was notable.
"I think that perceptions are crucial and interventions that are able to influence perceptions through environmental change are worth considering," said Sampson, author of the new Great American City: Chicago and the Enduring Neighborhood Effect.
Sampson's work in Chicago led him to develop a theory called collective efficacy. The idea is that when people feel connected to their neighbors and take ownership of the community, their willingness to intervene will reduce violence.
Frances E. Kuo, director of the Landscape and Human Health Laboratory at the University of Illinois at Urbana-Champaign, said the Penn study echoed her separate findings.
"In inner-city Chicago, we've found that residents of apartment buildings with some tree or grass cover reported feeling quite a bit safer than residents of identical apartment buildings without such green cover," Kuo said, and her team also "found that buildings with more tree and grass cover had significantly lower levels of crime and violence."
This is consistent with what the Pennsylvania Horticultural Society has seen in improving more than 7,500 vacant lots over 12 years, said Bob Grossmann, director of the initiative.
It is the most extensive greening program of its kind in the nation but still reaches only a fraction of the estimated 40,000 vacant lots in Philadelphia. Grossmann said the cleanup - grading, removing debris, erecting a low wooden fence, and planting grass and trees - costs $1 to $1.25 per square foot, plus 12 to 14 cents to maintain for the season, mostly from city and federal funds.
If that proves to have an impact on health, it is far cheaper than typical medical interventions, said Garvin, the new study author and an emergency medicine resident at the Hospital of the University of Pennsylvania.
Some of the most interesting elements of the study are still being analyzed.
In one, investigators walked around the neighborhood, before and after the greening, with residents who were wearing heart monitors. They are examining whether heart rates change when passing by a vacant lot.
"The thinking behind that was that people living in these neighborhoods express a lot of acute stress, which [can] become chronic stress, and that leads to [bad] cardiovascular health outcomes," Garvin said.
Contact Don Sapatkin at 215-854-2617 or firstname.lastname@example.org.